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Comprehensive Truck Size and Weight Study


	                Summary Report


  Phase I--Synthesis of Truck Size and Weight (TS&W) Studies and Issues

    	      Federal Highway Administration

	                March 1995

TABLE OF CONTENTS              	                         Page 

Executive Summary	                               ES - 1

Chapter 1.Introduction	                                    1  

	1.1	Purpose	                                    1  
	1.2	Study Plan	                            2  
	1.3	Federal TS&W Regulation Development	    3  
	1.4	Previous Studies	                    5  
	1.5	New Pressures and New Opportunities	    9  

Chapter 2.	Current TS&W Laws and Regulations	   11  

	2.1	TS&W Regulations and Trucking	           11  
	2.2	State and Local Law	                   11  
	2.3	U.S. Federal Law	                   12  
	2.4	Canadian and Mexican Laws	           12  

Chapter 3.	The Policy Environment	                   14  

	3.1	Policy Controls 	                   14  
	3.2	Highway Investment and Pricing 
                Considerations	                           16  
	3.3	Enforcement and Compliance	           17  
	3.4	Policy Options	                           17  

Chapter 4.	Current Knowledge of Policy Issues	   19  

	4.1	Pavement and Bridges	                   19  
	4.2	Roadway Geometry and Traffic	           26  
	4.3	Safety	                                   30  
	4.4	Permits, Pricing, and Enforcement	   35  
	4.5	Truck Costs and Logistics	           38  
	4.6	Truck Travel and Mode Share	           45  
	4.7	Environment and Energy Conservation	   48  

Chapter 5.	Knowledge Gaps and Research Needs	   51  

	5.1	Pavement and Bridges	                   51  
	5.2	Roadway Geometry and Traffic	           52  
	5.3	Safety	                                   52  
	5.4	Permits, Pricing, and Enforcement	   53  
	5.5	Truck Costs and Logistics	           53  
	5.6	Truck Travel and Mode Share	           54  


	This is the Summary Report of Phase I of the 
Comprehensive Truck Size and Weight (TS&W) Study announced by 
the Federal Highway Administrator in June 1994.  It 
summarizes 13 working papers prepared during Phase I.  The 
study is to be completed in three phases:  

	Phase I--Synthesis of TS&W Studies and Issues--assessed 
past policy studies and technical research.  Technical 
knowledge about relationships between TS&W policy controls 
and relevant evaluation and decision criteria was 
synthesized.  State and Federal TS&W regulations were 
summarized.  Research needs for later phases were identified. 
 Thirteen working papers were prepared examining the 
regulations and TS&W policy controls and: truck accidents, 
vehicle stability and control, pavements, bridges, roadway 
geometry, traffic operations, truck costs, shipper logistics 
costs, truck travel and mode share, enforcement, environment, 
energy, permits and pricing mechanisms. 

	Based on a review of the information, FHWA has 
identified several policy and technical issues for 
consideration in Phases II and III of the study.  No policy 
conclusions were drawn in Phase I and none are discussed in 
this report.  Consideration of policy options is being done 
in the later phases.  This interim report is being issued at 
this time to gather wide input from both the public and 
private sectors on the issues of importance to this study.  
	Phase II--a Preliminary Option Analysis--will evaluate 
specific policy options using existing databases and 
analytical tools (completion summer 1995).  

	Phase III--an Extended Impact Analysis--will expand the 
scope and depth of the policy analysis of PHASE II using new 
databases and analytical capabilities becoming available in 
late 1995 with projected completion by the end of 1996.  

	Based on a review of many policy and technical studies 
done over the last 10 to 15 years, the following are among the 
most important issues summarized in this Phase I report: 

.   There has been no significant change in Federal TS&W 
    law since 1982 except for the 1991 freeze of State 
    provisions for longer combination vehicles (LCV).  
    There have been many changes in factors interrelated 
    with TS&W laws over the past 20 years.  These include 
    growth in freight traffic, changes in freight 
    characteristics and origin-destination patterns, global 
    economics and trade, containerization and 
    intermodalism, economic deregulation, enhanced safety 
    programs, and truck equipment.

.   New questions about Federal TS&W law related to the 
    National Highway System (NHS), North American trade 
    harmonization, and retention of the 1991 freeze of 
    State LCV provisions should be addressed in Phases II 
    and III.  

ES - 1

.   There are a myriad of different TS&W regulations 
    affecting U.S. trucking emanating from local, State and 
    Federal Governments.  Many reflect considerations such 
    as differences in economic and industrial activities, 
    freight movements, infrastructure design 
    characteristics and status, traffic densities, mode    
    options and engineering philosophies.  The importance 
    of State TS&W regulations cannot be over-stated since 
    they govern trucking on the vast majority of U.S. road 

.   Federal law now regulates trucks by specifying basic 
    TS&W standards and excepting certain situations from 
    those standards by grandfather right and provision for 
    special permits.  Thus, current Federal regulations 
    state that the gross vehicle weight limit of a truck is 
    80,000 pounds on Interstate highways, but allow trucks 
    to carry international containers at more than 80,000 
    pounds, an exception to the standard.  

    Performance-standards regulation offers an alternative 
    approach.  Specifications are made as to acceptable 
    performance measures--in terms such as stability, 
    turning, or acceleration--with these measures then 
    becoming the basis of regulation either directly or 
    indirectly surrogate measures.  The performance-
    standard approach has been successfully applied to 
    substantial components of trucking in Canada.  While 
    there is a growing technical interest in this method, 
    there is also debate about details and about 

.   Consideration should be given to the enforceability of 
    policy options.  Enforcement of the existing relatively 
    simple regulations has proven difficult for many 

.   Developments in domestic containerization will effect 
    new demands on TS&W limits.  The intermodal 
    implications of TS&W policy options also need further 

.   The results of this study will provide a base of 
    knowledge that can be used for the ongoing trilateral 
    consultations on vehicle weights and dimensions 
    required by the North American Free trade Agreement 

Chapter 5 identifies several research topics that will be 
important to carry out during Phases II and II to more 
definitively resolve TS&W policy options.  

ES - 2


1.1	Purpose

On June 14, 1994, during testimony before the U.S. House of 
Representatives Committee on Public Works and 
Transportation's Subcommittee on Surface Transportation, 
Federal Highway Administrator Rodney E. Slater made a 
commitment to conduct a Comprehensive TS&W Study.  Stating 
that the FHWA had not made a "... comprehensive effort to 
analyze truck size and weight issues for the last 30 years 
...,"  he added, "The time has come to revisit this issue and 
to do it in a way that is comprehensive, ... analytical, and 
well thought out ... to look at it holistically ...".  
Further, he said that "I believe a fundamental reexamination 
of all vehicle size and weight issues is necessary."  

Historically, TS&W regulations have been driven by a concern 
for national uniformity and good highway system stewardship--
matching vehicle weights and dimensions with the existing 
capacity of the public infrastructure and with mechanisms for 
cost recovery.  At times, new pavement and bridge design 
standards have been adopted by the States to better match the 
weights and dimensions of the vehicles being allowed to 
operate on their highways.  However, avoidance of premature 
degradation of that infrastructure with its attendant strain 
on public resources continues to be a major concern.  More 
recently, as technology and shipper demand have joined to 
make larger and heavier trucks a reality, concerns for 
highway safety and loss of rail service have become 
increasingly important, especially with regard to longer 
combination vehicles (LCV).  

A shift of some TS&W regulatory authority from the States to 
the Federal Government occurred at the start of the 
Interstate construction era in the 1950's, and since then, 
the distribution of this shared authority has shifted back 
and forth.  Now, as the Interstate construction era draws to 
a close, the transportation community is again reassessing 
the Federal role in the context of future highway 
transportation needs.  

The ultimate goal of the Comprehensive TS&W Study is to 
estimate the effects of various elements of regulatory policy 
on a transport system in transition as it evolves to serve a 
modern global economy.  New capabilities and opportunities 
exist with new distribution and electronic systems.  The 
impacts of changing logistics costs, production strategies, 
and shipping patterns must be balanced with the needs and 
concerns of carriers, managers of infrastructure, shippers, 
consumers, and the traveling public.  TS&W policy touches 
upon public concerns such as safety, infrastructure design 
and wear, States' rights and national uniformity, 
environment, energy use, intermodal competition, and cost 
recovery.  Finally, these issues must be evaluated at several 
levels--local, State, regional, national, and international. 

1.2	Study Plan

The following three phase study plan was developed to address 
the issues related to possible changes in Federal TS&W 
provisions.  Additional information on this study is 
available in a Federal Register notice published on February 
2 (60 FR 6587).  

Phase I, TS&W Synthesis, has assessed past policy studies and 
research findings.  This report describes the current 
knowledge of the technical relationships between TS&W policy 
controls and their related issues.  The history of State and 
Federal TS&W regulation are reviewed, State and Federal TS&W 
regulations are summarized, and knowledge and research gaps 
on TS&W issues are identified and prioritized.  TS&W studies 
completed within the last 15 years and more recent research 
not covered in these studies have been synthesized in 13 
working papers that cover:  

	Pavement and bridge wear
	Roadway geometry
	Traffic operations
	Truck operating costs
	Shipper logistics costs
	Truck travel
	Mode share
	Energy conservation
	Permits and pricing mechanisms
	Existing TS&W regulations  

These working papers are available in FHWA Docket No, 95-5 
established for this study.  

Phase II, a Preliminary Option Analysis, will evaluate, on a 
limited basis, specific policy options using existing 
databases.  It is preliminary because new data for a 
comprehensive analysis of TS&W issues, such as commodity flow 
information, will only become available in late 1995.  
Therefore, Phase II policy options will include appropriate 
caveats regarding the limitations of earlier studies.  The 
analysis will be as comprehensive as possible, but at a 
minimum, it will include the impacts of changes in Federal 
TS&W provisions on safety, infrastructure, and economic 
productivity.  This phase will be completed during the summer 
of 1995.  

Phase III, an Extended Impact Analysis, will use the data and 
new tools that become available in 1995 and 1996 to prepare 
in-depth analyses of the Phase II policy options.  It will 
incorporate results from a parallel cost allocation study 
that FHWA is undertaking to determine whether the various 
highway users, including heavy vehicles, are paying their 
fair share into the Highway Trust Fund.  Specific policy 
options will be analyzed using improved 


information on freight flows and truck use and will address the 
full range of costs and benefits estimated to derive from these
options.  The study will be completed by the end of 1996.  

1.3	Federal TS&W Regulatory Development

While State and local laws govern trucking on the majority of 
the Nation's highways, Federal law directly governs and 
indirectly influences a substantial amount of total trucking 
activity.  The milestones in Federal TS&W regulation are:

In 1956 Congress legislated maximum axle weight, gross 
vehicle weight, and width limits for trucks operating on 
Interstate highways.  Congress adopted the weight limits 
recommended in 1946 by the American Association of State 
Highway Officials (AASHO), now the American Association of 
State Highway and Transportation Officials (AASHTO): 18,000 
pounds on a single axle, 32,000 pounds on a tandem axle, and 
73,280 pounds gross weight.  The Federal law also authorized 
States to allow operation on Interstate highways beyond the 
specified limits, but only if such operation was legal in the 
State prior to July, 1 1956.  This became known as a 
"grandfather right." 

In 1975 Congress authorized higher axle and gross vehicle 
weights on the Interstate System.  However, States were not 
required to adopt these higher limits.  Some did not.  In 
addition, a "Federal Bridge Formula" (Bridge Formula B) was 
imposed limiting the gross weight of any group of axles to 
the lesser of the cap or a value determined by the number of 
axles and the distance between them; the heavier the weight 
the greater the spacing required.  States with 
"grandfathered" bridge formulas (in effect before 1975) did 
not have to enforce the Federal formula.  

In 1982 Congress required that all States allow on their 
Interstate highways loads of 20,000 pounds on single axles, 
34,000 pounds on tandem axles, 80,000 pounds total for a 
vehicle, and enforce the Federal Bridge Formula.  The width 
limit was increased to 102 inches.  States were required to 
allow 48-foot semitrailers and double combinations of two 28-
foot trailers.  The Federal length and width provisions were 
extended beyond the Interstate System to the designated 
National Network (NN) for large trucks and related access 
roads.  States having grandfather rights were authorized to 
determine what vehicles and operating situations would be 
considered "grandfatherable".

Grandfather Rights

There are three different grandfather clauses in Section 127, 
Title 23, U.S.C.  The first, enacted in 1956, deals 
principally with axle weights, gross weights, and permit 
practices; the second, adopted in 1975, applies to bridge 
formula and axle spacing tables; and the third, enacted in 
1991, ratified State practices with respect to LCVs.  


The vehicle weight limits--18,000 pounds on a single axle, 
32,000 pounds on a tandem axle, and 73,280 pounds gross 
weight--enacted in 1956 were to protect Interstate System 
pavements and bridges from damage or premature wear caused by 
excessively heavy trucks.  Some States, however, already 
allowed trucks with axle or gross weights in excess of those 
values.  The grandfather clause was therefore enacted to 
avoid a rollback of vehicle weights legal in those States, 
while the AASHO standard set an upper limit on weights 
otherwise allowable.

In response to energy use concerns, the Federal-Aid Highway 
Amendments of 1974 increased the allowable single axle, 
tandem axle, and gross weight limits on the Interstate to 
20,000, 34,000 and 80,000 pounds, respectively, although not 
all the States adopted these limits.  The bridge formula and 
a corresponding grandfather clause were added at the same 
time.  This second grandfather clause allows States to retain 
any bridge formulas or axle spacing tables in effect on 
January 4, 1975, which allowed greater vehicle weights at the 
same axle spacing than the new Federal formula.  

The Surface Transportation Assistance Act of 1982 included an 
amendment to Section 127 introduced by Senator Symms.  The 
language on withholding of Federal-aid funds was modified to 
read as follows (Symms amendment underlined):

     This section shall to be construed to deny 
    apportionment to any State allowing the operation 
    within such State of any vehicles or combinations 
    thereof which the State determines could be lawfully 
    operated within such State on July 1, 1956, except in 
    the case of the overall gross weight on any group of 
    two or more consecutive axles (that is, the bridge 
    formula), on the date of enactment of the Federal-Aid 
    Highway Amendments of 1974.

Sections 1023 and 4006 of the Intermodal Surface 
Transportation Efficiency Act of 1991 froze the operation of 
LCVs, defined as a tractor and two or more trailers or 
semitrailers operating on the Interstate with a gross weight 
in excess of 80,000 pounds.  More specifically, it provided 
that LCV combinations which were in actual and lawful 
operation under State law on June 1, 1991, could remain in 
operation, provided the State continued to enforce the 
weight, length, and route restrictions and any other 
limitations then imposed on these vehicles.  

North American Free Trade Agreement (NAFTA)

Senate Report 102-351, which accompanied the 1993 
Appropriations Act for the Department of Transportation and 
Related Agencies, requested the FHWA to report on the status 
of discussions relative to the NAFTA on TS&W, and to include 
a summary of potential highway related impacts from 
implementing changes to U.S. TS&W limits.  In response, the 
FHWA reported the Agreement has no provisions that raise U.S. 
Federal or State limits on TS&W.  It does establish a process 
for the United States, Canada, and Mexico to work toward 
compatible technical and safety standards.  Truck weights and 
dimensions are 


technical standards and a part of the NAFTA standards 
harmonization work plan.  The NAFTA establishes the 
Land Transportation Standards Subcommittee (LTSS) which will 
have delegations from the three countries consult on TS&W and 
other standards.  As a part of the compatibility work plan, 
the LTSS component on weights and dimensions is to work for 3 
years to attempt to make truck weight and dimension measures 
and related requirements compatible.  

1.4	Previous Studies

Changing concerns, circumstances and opportunities have 
caused numerous investigations of TS&W matters by 
governments, industry, interest groups, and individuals.  
Recent national and international research of particular 
significance to TS&W policy today in the United States are 
discussed in the following sections:  

Federal Studies

Earlier, Federally-mandated studies were reported in:

1941  Federal Regulation of the Sizes and Weight of Motor 
      Vehicles:  Congress instructed the Interstate Commerce 
      Commission to investigate the need for Federal 
      regulation of the sizes and weight of freight-carrying 
      motor vehicles engaged in interstate or foreign 
      commerce.  The principal findings were: (1) State 
      limits were a costly obstacle to interstate trade, (2) 
      Federal intervention was accordingly warranted but only 
      in response to specific complaints regarding particular 
      situations, and (3) considerations of safety and 
      convenience do not unto themselves justify Federal 

1964  Maximum Desirable Dimensions and Weights of Vehicles 
      Operated on the Federal-Aid Systems:  In the Federal-
      Aid Highway Act of 1956, Congress instructed the 
      Secretary of Commerce to report on research and make 
      recommendations regarding maximum desirable weights and 
      dimensions for vehicles operated on the Federal-aid 
      highway systems, including the Interstate System.  The 
      principal recommendations--predicated on an assumption 
      of continued financial support--were: (1) not to make 
      recommendations for Federal vehicle standards for 
      Federal-aid primary and secondary systems and their 
      respective urban extensions (because of lack of 
      relevant information); (2) retention of the current 
      width and axle limits, removal of the GVW cap, and 
      adoption of a Bridge Formula A for a 3 year period; 
      (3) introduction of maximum length limits for single 
      and combination units, and a height limit; (4) 
      introduction of performance standards respecting 
      maximum weight-to-power ratio, minimum brake system 
      performance, and linkage mechanism requirements for 
      combinations; and (5) after 3 years, increase in the 
      width limit and axle weight limits, and adoption of 
      Bridge Formula B (a formula more permissive than A).  


1981  An Investigation of Truck Size and Weight Limits:  In 
      the Surface Transportation Assistance Act of 1978, 
      Congress instructed the Department of Transportation to 
      examine--among other things--the need for, and 
      desirability of, uniformity in maximum truck size and 
      weight limits throughout the United States.  Five 
      categories of changes in limits were assessed--namely 
      grandfather clause elimination, barrier elimination, 
      uniformity, rollback to pre-1974 limits, and increases 
      in limits.  The study examined the benefits and costs 
      to the U.S. economy and society as a whole, as well as 
      to individual interest groups associated with a series 
      of TS&W scenarios.  

1985  Feasibility of a Nationwide Network for LCVs:  In the 
      Surface Transportation Assistance Act of 1982, the 
      Congress mandated a study on the potential benefits and 
      costs that could be anticipated from the establishment 
      of a nationwide network for LCVs.  The study report 
      concluded that: (1) there is no compelling evidence 
      that LCVs are so desirable that increased Federal 
      intrusion into State size and weight regulation 
      authority was justified; and (2) the transportation 
      efficiency gains were potentially substantial, but they 
      are offset by safety concerns, losses in rail 
      productivity, and high initial investment to realize 
      the potential efficiencies.  

1986  Longer Combination Vehicle Operations in Western 
      States:  In 1985, the Senate Appropriations Committee 
      called for a study of LCV operations in the Western 
      States.  This study reported that the productivity 
      benefits of allowing LCVs to operate more widely and at 
      higher weights are unquestioned.  The report noted the 
      Department's commitment to work with the States and 
      trucking groups to explore ways to improve the 
      efficiency and safety of trucking.  The Department 
      would be better prepared to evaluate TS&W initiatives 
      and enhance the productivity of LCVs, once ongoing 
      research and congressional studies were completed.  

Transportation Research Board (TRB) 

The TRB published two major TS&W studies in 1990.  The first, 
Truck Weight Limits: Issues and Options (Special Report 225), 
was requested by the Congress in the Surface Transportation and 
Uniform Relocation Assistance Act of 1987.  It recommended: 
(1) establishment of a new Federal bridge formula, (2) 
prohibition of expanded grandfather claims for vehicles that 
exceed existing Federal limits, (3) establishment of State 
permit programs for trucks that exceed the Federal gross 
weight limit of 80,000 pounds (but only if accompanied by 
fees to cover additional public costs and restrictions to 
promote improved safety), (4) increased truck weight 
enforcement, (5) regional cooperation among States in 
standardizing limits and permit practices.  There has been no 
implementation of any of these recommendations except for the 
last, which triggered a project undertaken cooperatively by 
the FHWA and AASHTO.  

The second, New Trucks for Greater Productivity and Less Road 
Wear: An Evaluation of the Turner Proposal (Special Report 
227), was requested by AASHTO.  It evaluated an approach to 
TS&W regulation wherein motor carriers could voluntarily 
choose between using existing 


equipment or adopting new "Turner trucks" with lower axle 
weights (to reduce pavement damage); higher GVW (to increase
productivity); and superior stability, control and operational 
properties (to enhance safety).  It identified a series of 
Turner trucks and detailed, innovative regulations for them.  
These proposed regulations addressed: (1) tire and axle limits,
(2) a new bridge formula, (3) performance-related provisions 
concerning off-tracking, (4) configuration-specific regulation
differences, (5) prohibition of C-trains and self-steering 
axles, (6) prohibition of lift axles, (7) a requirement for 
anti-lock braking on tractor axles, (8) a performance-related 
gradeability standard, (9) operating routes, and (10) special 
driver qualification requirements.  Congress took no action 
on these recommendations.  

General Accounting Office (GAO)

The GAO has conducted three investigations on TS&W-related 
matters since 1992--all dealing with LCV considerations.  The 
observations, conclusions and recommendations from the 1994 
report, Longer Combination Trucks: Potential Infrastructure 
Impacts, Productivity Benefits, and Safety Concerns, are: 

1.    Nationwide use of LCVs on interstates would require a 
      one-time infrastructure investment of up to $3.5 
      billion (FHWA estimate) and yield an annual reduction 
      in trucking costs of $3.4 billion (industry estimate). 
      Principal beneficiaries would be the large, national 
      small package and less-than-truckload (LTL) carriers.

2.    Limited data show that LCVs have not been a safety 
      problem on the western highways and eastern turnpikes 
      where they operate.  

3.    "(I)dentified operational characteristics of LCVs ... 
      could make them a greater safety risk than single-
      trailer combinations if allowed on more-congested 

4.    The American Association of Railroad model used for 
      estimating rail to truck diversions that would result 
      from greater LCV use has significant shortcomings 
      (insensitive to railroad productivity gains; assumes 
      that truckload (TL) traffic will generally convert to 
      using turnpike doubles).  

5.    Expanded use of LCVs should be permitted by exception 
      to the current freeze, based on State requests and 
      State commitments regarding suitability, cost recovery 
      and enforcement. 

The two other reports: (1) Longer Combination Trucks: Driver 
Controls and Equipment Inspection Should be Improved, and (2) 
Truck Safety: The Safety of Longer Combination Vehicles is 
Unknown, confirmed the difficulty of rendering a clear, 
definitive conclusion about the on-road safety performance of 
LCVs relative to other truck types.  They reflect the 
longstanding data limitation problems that have made it 
impossible to definitively detect differences in on-road 
safety performance that can be associated with differences in 


laws.  This is not to say that TS&W law does not affect 
handling and stability performance characteristics of trucks; 
it does.  However, acceptance of this reality may provide the 
basis from which useful consideration can be given to how 
TS&W law might be deployed to improve the inherent safety-
related performance of trucks, even though these improvements 
may not be irrefutably detected in a statistically convincing 
manner on the road.  


The AASHTO Subcommittee on TS&W has been working since July 
1992 on the development of TS&W recommendations to be made to 
the AASHTO Joint Committee on Domestic Freight Policy, later 
incorporated into the AASHTO Special Committee on Intermodal 
and Domestic Freight Policy.  The Subcommittee drafted the 
following "Policy Premises" to guide the development of its 

	Long term financial stability of highway infrastructure
	TS&W limits be based on full public costs and benefits
	Need to understand cost responsibility of large trucks
	Safety should continue to improve
	Insufficient safety data to justify significant 
        expansion of large truck usage
	Need to better control incremental TS&W increases
	Retain ISTEA freeze for time being
	Need national context for TS&W regulation and taxation
	Require systematic calculations of productivity gains
	Continue to reduce administrative burdens
	Support environment and energy policies

The Joint Committee will shortly release for publication the 
Subcommittee's report with comments and its 12 Freight Policy 

The TRB and the National Cooperative Highway Research Program 
have two completed and several ongoing studies to support the 
AASHTO effort to develop new TS&W and freight policies.  The 
completed studies are "Synthesis on the Impacts of Truck Size 
and Weight on the Transportation System and the Economy" and 
"White paper on the Feasibility of Longer Combination 
Vehicles."   The ongoing studies include: "The 
Characteristics and Growth of Freight Demand," "Public Policy 
for Rail and Truck Competition," "Institutional Arrangements 
and Compatibility of Federal/State Truck Regulations," and 
"Corridor Analysis of Highway and Bridge Capacity."

International Studies

Canada carried out a major TS&W research project under the 
auspices of the Roads and Transportation Association of 
Canada (called the RTAC Study) in the 1980s.  It was co-
sponsored  by the Federal and Provincial Governments and 
industry.  The research examined infrastructure, stability 
and control, and economic aspects of TS&W in Canada for a 


range of new and innovative truck combinations.  Unlike 
similar research efforts in most countries, this one actually 
culminated in a significant change of regulations agreed to 
and implemented by all provinces in a Memorandum of 
Understanding in 1988.  This change in regulations has in 
turn spurred the broad acceptance of new, more productive, 
and safer trucks across the country.  Unique to this 
regulation package is the fact that several aspects of it are 
founded on "performance" requirements, in particular, 
relating to stability and control and off-tracking.  The new 
regulations have led to dramatic changes in the fleet mix in 
certain parts of the country, particularly in the west.

Mexico's Transportation Institute, in the Secretariat of 
Communications and Transportation, is conducting a variety of 
research projects in the areas of pavement management, the 
economics of TS&W regulations, and truck-pavement 

The Organization for Economic Cooperation and Development 
(OECD) Dynamic Interaction Vehicle - Infrastructure 
Experiment (DIVINE) project, to be completed in 1996, is an 
international cooperative research project focusing on the 
interaction of live axle loads from heavy trucks with 
pavements and bridges.  The United States is one of 14 
countries involved in the research.  The project will provide 
a scientific basis for truck suspension evaluation, and for 
understanding the effects of vehicle vertical response on low 
frequency bridges and flexible pavements.  

Other Initiatives

The Trucking Research Institute of the American Trucking 
Association has commissioned the Iowa Motor Transportation 
Center to conduct a study of performance-based size and 
weight standards.  This study commenced in November 1994. 

The FHWA and National Highway Traffic Safety Administration 
are jointly conducting studies on the safety of LCV 
operations in response to the ISTEA.  These studies will 
assess: (1) the incremental stress on fatigue that LCV 
drivers experience, if any, compared to drivers of standard 
combinations, and (2) the practicality of using antilock 
brakes and double drawbar dollies on multiple-trailer 
combinations.  The reports will be delivered to Congress in 
December 1995.  

1.5	New Pressures and New Opportunities

No significant change in Federal TS&W law has occurred since 
1982, except for the freezing of LCV operating rights in 
1991.  Since 1982, major changes and developments have 
occurred in many areas of import to TS&W policy.  They 
include: (1) changes in freight movements due to growth, new 
origins and destinations, increasing use of containers and 
double-stack trains, and just-in-time delivery requirements; 
(2) changes in global economics and trade patterns especially 
given the North American Free Trade Agreement and the General 
Agreement on Tariffs and Trade; (3) increasing traffic 
volumes; (4) fall-out from 


deregulation of the transportation industry; (5) improved motor
carrier safety regulation through the Commercial Vehicle Safety
Alliance and the FHWA Motor Carrier Safety Assistance Program; 
and (6) vehicle equipment improvements such as radial tires, 
improved brake systems, and 53-foot semitrailers.  

In addition, important new questions concerning Federal TS&W 
law have emerged:

.  How should Federal TS&W provisions relate to the NHS?
.  How should harmonization goals for NAFTA be approached?
.  Should the LCV freeze imposed by ISTEA be permanent?  

These changes, developments and questions need comprehensive 
consideration in conjunction with the issue of cost 
allocation and revenue generation.  Particularly important to 
a comprehensive study are developments in the areas of truck 
use, commodity flow, highway condition data and truck-
pavement interaction, logistics, truck travel and mode share, 
and highway cost allocation analytical capability.  

Lastly, what future role should the Federal Government play 
in TS&W regulation.  The question of Federal involvement was 
at the heart of the first Federal review of TS&W matters by 
the Interstate Commerce Commission in 1941.  Today the 
Federal Government specifies certain standards, reviews State 
practices, and monitors State enforcement activities and 
exercise of grandfather rights.  Possible alternatives to the 
existing Federal role are to: (1) gradually disengage from 
TS&W regulation, (2) control TS&W in different ways such as 
through performance regulation, (3) modify impacts or need by 
different investment or pricing policies, and (4) establish 
uniform guidelines for regional and State regulations.  



Trucking in the United States is subject to TS&W regulations 
emanating from the local, State, and Federal governments.  
The importance of State and local regulations cannot be over-
stated.  These regulations govern trucking on the vast 
majority of U.S. road mileage and may indeed govern the vast 
majority of trucking activity itself.  Some of these 
regulations are grandfathered exceptions to Federal law.  

In Canada, the laws of the individual provinces govern, but 
these includes a common set of regulations on major highways 
as agreed upon by the Provinces.  Operations into Mexico are 
subject to Federal law, the standards for which vary for the 
four different classes of Federal roads.  

2.1	TS&W Regulations and Trucking

TS&W regulations are a significant determinant of what truck 
configurations are available to operators; and how trucks 
impact the infrastructure, the economy, highway safety, and 
the environment.  Many other factors--including freight 
characteristics, shipment sizes, industry considerations, 
driver requirements--also influence the design and use of a 
vehicle, but none to the extent of TS&W requirements.  

TS&W regulations define the envelope (maximum length, width, 
and height) within which trucks are to fit and the maximum 
weight they are to observe.  Most of the time, most trucks 
operate well within the boundary conditions.  Some trucks 
regularly operate at or near the boundaries.  Some operate 
beyond the boundaries some of the time.

If a truck is operated within only one TS&W regulatory regime 
for example within one State, then it is optimized to that 
regime.  A trucker confronted with multiple TS&W regimes has 
three choices: (1) to select a "least common denominator" 
vehicle and operating strategy; (2) to select a vehicle or 
operating practice which can be modified enroute as needed 
(for example, remove a trailer, reduce the load, move an axle);
or (3) to attempt to circumvent the law.  The complexity of 
the truck regulatory and operational environments continues to
increase, as the role of trucking pervades nearly every aspect 
of the increasingly global economy.

2.2	State and Local Law

The sizes and weights of vehicles have been regulated by 
State and local law since the early part of the century.  
Over the years, these regulations have been changed many 
times in response to needs and circumstances.  Change 
continues--often without Federal involvement or influence. 


Working Paper 14, prepared for this study, details current 
State regulations.  Broadly speaking: (1) many State 
provisions differ from Federal provisions, (2) there are many 
regulation differences among the States, and (3) there are 
more regulatory differences than ever.  These differences 
exist because of the differences in economic and industrial 
activities; freight movements; infrastructure design 
characteristics and status; traffic densities; mode options; 
engineering philosophies; and choices of the different 
locales, States, and regions of the Nation.  

The differences tend to reflect population and traffic 
density considerations.  The dense areas in the Northeast 
tend to favor smaller trucks with highly concentrated loads, 
while low density areas, mostly in the west, favor larger 
trucks with less concentrated loads.  These differences are 
apparent in the various State provisions grandfathered under 
the Federal law.

2.3	U.S. Federal Law

The Federal Government first became involved in TS&W 
regulation at the start of the Interstate era in the 1950's 
when maximum axle and vehicle gross weight and width limits 
were set trucks using that system.  In 1975, the weight 
limits were raised, except that 
the bridge formula was imposed to insure that the vehicle 
load was distributed to avoid excessive overstressing of 
bridges. In 1982, minimum length limits were enacted for 
semitrailers and trailers in twin-trailer combinations.  The 
width limit was also increased from 96 to 102 inches.  The 
current U.S. Federal TS&W law has the following limits:

    -	20,000 pounds for single axles. 
    -	34,000 pounds for tandem axles. 
    -	Application of Bridge Formula B for other axle 
        groups up to the maximum of 80,000 pounds for gross 
        vehicle weight (GVW). 
    -	102 inches for vehicle width 
    -	48 feet (minimum) for semitrailers in a semitrailer 
    -	28 feet (minimum) for trailers in a twin-trailer 

Federal truck weight law applies to the Interstate System and 
vehicle size law applies to the designated NN which includes 
the Interstate System.  The NN was designated under the 
authority of the same 1982 Act that established the above 
size limits.  

2.4	Canadian and Mexican Laws

In Canada, the individual provinces and territories are 
responsible for TS&W regulations.  There is no Federal law.  
However, all jurisdictions have adopted a national set of 
"RTAC" regulations for operations on primary highways 
throughout the country.  These regulations were developed 
from a research program in the mid-1980s directed at 
improving truck 


safety, productivity and road-friendliness.  Several aspects 
of these regulations are derived from desired performance 
criteria relating to such matters as off-tracking and roll 

Compared to the U.S. Federal law, the Canadian regulations 
established as a result of the Road and Transportation 
Association of Canada (RTAC) study, specify:

    -	12,125-pound steering axle limit 
    -	37,479-pound tandem-axle limit 
    -	46,297- to 52,911-pound tridem axle limit--depending on
        how far apart the axles are spread 
    -	Substantially higher (up to 137,500 pounds) GVW limits 
        (which vary by truck configuration to encourage the use
         of more stable vehicles) 
    -	75.5-foot overall vehicle length limit
    -	53-foot maximum semitrailer length limit 
    -   Wheelbase, kingpin and overhang limits (to control 
    -   Minimum interaxle spacings (to control bridge loadings)

In Mexico, the regulations applicable on national highways 
are established by the Federal government.  Compared to the 
U.S. Federal law, the Mexican regulations specify:

    -	14,330-pound steering axle limit 
    -	42,990-pound tandem-axle limit 
    -	49,604-pound tridem axle limit  
    -	Substantially higher (up to 136,600 pounds) GVW limits
        (which vary by truck configuration 
    -	68.2-foot overall length limit for semitrailer 
    -	102.7-foot overall vehicle length limit for double 
        cargo unit combinations
    -	Minimum interaxle spacings (to control bridge loadings)


Click HERE for graphic.

               Table 1 - Basic Standards

	                                   Federal	State 							
			                    Law	         Law
Vehicle Weight Limits 
   - tire-related								
	  number of tires	     	    No	         Some	
	  tire load limits 	            No		 Some	
	  load distribution between tires   No	  	 None	
   - axle-related								
          load limits by axle type  	    Yes		 All	
          load distribution between axles  
          in a group	                    No		 Some	
          suspensions                       No		 None	
          lift axles			    No		 Some	
   - gross vehicle weight-related					
          bridge formula		    Yes		 All	
	  cap				    Yes	         All   
Vehicle Dimension Limits
   - height				    No	         All	
   - width			    	    Yes		 All	 length									
	  single unit		            No		 All	
	  semitrailer                       Yes		 All	
	  trailer                           Yes		 All	
	  combination	                    No		 Some 
Vehicle Specifications
   - configuration			    No		 Some	
   - body type                              No		 None	
Equipment Specifications							
   - safety-related	
		hitching 		    Yes	         No	
		weight distribution 	    No		 Some	
		power/weight 		    No	 	 Some	
   - off tracking-related						
		kingpin 		    No		 Many	
 		hitching 		    No	         None	
Operational Restrictions
   - area (local, state, region, routes)    No		 All	
   - facility-related (bridge posting)	    No	  	 All	
   - seasonal, day-of-week, time-of-day	    No		 Some	
   - weather conditions		    	    No		 Some	


Exemptions to basic standards are the second most common type 
of policy control.  Every jurisdiction has found it desirable 
in cases regarding major local industries such as coal, 
timber, and agriculture and necessary in others to provide 
exemptions, by regulation, permit, policy and tolerances. 

Performance standards are a form of policy control that 
involves specifying minimum or maximum acceptable levels of 
performance (rather than absolute physical limits) regarding 
matters such as:

	Off-tracking envelope
	Acceleration capability
	Speedability on grades
	Speed control downgrade
	Lane change capability
	Braking capability 
	Crash avoidance maneuvering
	Rollover threshold
	Load equivalency factors (LEFs) per truck
	Passenger car equivalencies (PCEs) per truck

Selected performance standards have been utilized in some 
countries, but have not been adopted widely in the United 
States.  A general consensus about which performance measures 
are most critical is beginning to emerge in the technical 
community.  This provides opportunities to improve the 
rationality of TS&W regulation.  However, details on how to 
enforce performance standards on day-to-day trucking need to 
be resolved to make them possible.  

3.2	Highway Investment and Pricing Considerations 

An alternative way to deal with the intent of certain TS&W 
regulations, such as axle load limits to protect pavement, is 
to change investment principles and pricing.  For example, 
additional investment increments on a new or reconstructed 
pavement can render the pavement less sensitive to truck 
loads.  Similar alternatives are available for new bridges or 
bridge strengthening.  Life cycle cost analysis often shows a 
benefit for higher initial design standards.  

Control by pricing is a policy mechanism that entails 
controlling trucks, their loads and their operations by 
requiring them to pay for the full costs they impose.  
Controlling truck weights entirely by pricing is not a likely 
option for the near term.  Technological developments may 
facilitate such an approach in the future.  There is 
increasing interest in this approach, not for just 
controlling TS&W, but for traffic congestion and other 

Even without full cost pricing, truck size and weight policy 
and highway user fee issues should be periodically evaluated. 
 Pavement and bridge costs attributable to heavy vehicles 


will be impacted by any changes in size and weight policy 
changes.  Significant changes in size and weight limits 
should be accompanied by an assessment of appropriate changes 
in highway user fees.  

In its June 1994 report, "Highway User Fees:  Updated Data 
Needed to Determine Whether All Users Pay Their Fair Share," 
the GAO recommended that the FHWA conduct a formal cost 
allocation study "to determine whether all highway users are 
paying their fair share of Federal highway costs and to 
ensure that FHWA and the Congress have up-to-date information 
when making future decisions affecting Federal highway user 
fees."  Other organizations including the AASHTO also have 
called for a new Federal highway cost allocation study.  A 
Highway Cost Allocation Study update is being conducted in 
parallel with this Comprehensive TS&W Study.  A notice 
announcing the cost allocation study was published in the 
February 10, 1995 Federal Register.  

3.3	Enforcement and Compliance

In developing and implementing new TS&W regulatory concepts, 
the "enforceability" question must be addressed.  Most 
jurisdictions today have trouble effectively enforcing even 
relatively simple regulatory requirements.  Making 
requirements more technical and sophisticated without 
reference to their enforceability may prove counter-
productive.  "Without effective enforcement ... weight limit 
laws are meaningless," the TRB noted in Special Report 225.  

3.4	Policy Options

This section describes categories of TS&W policy options 
available to the Federal Government.  The categories are:  
(1) Federal role alternatives, (2) changes in scope of 
Federal TS&W Policy, (3) changes in limits and other 
standards, and (4) exceptions to Federal limits and other 

Federal Role Alternatives

The question of Federal involvement was at the heart of the 
first Federal review of TS&W matters by the Interstate 
Commerce Commission in 1941.  At that time, major opposition 
to Federal involvement came first and foremost from the 
American Association of Railroads, and secondly the States.  
The report observed "that Federal intervention ... should be 
... resorted to only in particular cases and upon clear proof 
that an unreasonable obstruction to interstate commerce 

Today, the Federal Government specifies certain standards, 
reviews State practices, and monitors State enforcement 
activities and exercise of grandfather rights.  Possible 
alternatives to the existing Federal role are to: (1) 
gradually disengage from TS&W 


regulation, (2) control TS&W in different ways such as through
performance regulation, (3) modify impacts or need by 
different investment or pricing policies, and (4) establish 
uniform guidelines for regional and State regulations.  

Changes in Scope of Federal TS&W Policy

Policy options in this category would deal with the scope of 
Federal TS&W policy in terms of vehicle types, highway 
systems, and Federal versus State roles.  They would ensure 
that Federal TS&W policies are applied only to the extent 
necessary to achieve Federal objectives.  

This study is in partial response to a proposal in the 103rd 
Congress to extend Federal TS&W controls to the proposed NHS 
established by the ISTEA of 1992 and to freeze existing State 
trailer length limits.  There is concern that the widespread 
implications of such a sweeping proposal demand that any 
decision be made only after close examination of both public 
and private sector concerns and from the point of view of 
impacts on the safety and efficiency of the total transport 
system.  A primary issue is whether Federal truck weight 
limits should apply to the NHS.  Federal truck size limits 
already apply to most highways on the NHS as well as on the 
National Network for large trucks mandated by the Surface 
Transportation Assistance Act of 1982.  Exceptions to this 
are in those States that have a limited set of National 
Network routes, which are eastern States for the most part.  

Changes in Limits and Other Standards

These options would cover the weight and dimension limits and 
other standards for vehicles and operations needed to ensure 
that Federal policy objectives are met.  

Exceptions to Federal Limits and Other Standards

These options would address how and under what conditions, if 
any, exceptions to the Federal limits and standards should be 
allowed.  They would address grandfather rights, Federal 
involvement in oversize and overweight permitting, and 
regional exceptions to national standards.  



4.1	Pavement and Bridges


Areas of extensive recent research on pavement and TS&W 
regulation are: 

.    Changes in tire types, pressures, sizes, and loading 
     characteristics and their implications for pavement wear.  
.    The relative effects of different axle configurations and 
     loads on pavement damage.
.    Truck-pavement interaction, vehicle dynamics, and the role 
     of suspension systems.
.    Long-term pavement performance.

The following issues are of particular interest to Federal 
policy considerations at this time.

ISSUE:  Current Axle Load Limits

Axle limit standards and variations:  Federal law specifies 
single- and tandem-axle weight limits, of 20,000 and 34,000 
pounds respectively.  The limits were formally recommended in 
the 1964 TS&W Report to Congress.  They are the lowest axle 
weight limits imposed on major highways in the world 
(including Canada and Mexico).  (Differences in design 
philosophy and pavement life expectations explain part of the 
difference in axle weight limits among jurisdictions).  One 
or both of the Federal axle limits are surpassed by the laws 
of 25 States.  Higher single and/or tandem axle limits are 
permitted on Interstates in 12 States (by grandfather 
rights).  Permits and/or tolerance policy routinely allow 
Federal limits to be exceeded in most States.

The technical origin of the 34,000 pounds value of the tandem 
limit is uncertain.  The original pavement-related research 
work behind the establishment of this limit dealt 
with a 35,000-pound limit.  Pavement and productivity 
benefits could be realized by increasing tandem axle loads 
without making any other changes in the Federal law.  For 
example, increasing the tandem load to 35,000 pounds within 
an 80,000 pounds GVW cap could reduce pavement damage caused 
by a fully loaded 5-axle tractor-semitrailer by 
10 percent (by transferring load from the heavily-loaded, 
pavement-damaging front axle).  Coincidentally, this change 
could increase the potential payload weight capacity of this 
truck by 4 percent while creating no identifiable, measurable 
negative effects.

Wide-spread tandem axles:  There is increasing use of wide-
spread (10 feet) tandem axle groups, particularly in flat-bed 
heavy haul operations.  These axles are allowed to be 
loaded at single axle limits.  They offer two key benefits to 
five-axle tractor-semitrailers usage: (1) full achievement of 
the 80,000 pound GVW cap, and; (2) flexibility in load 


distribution.  But they do so with undesirable pavement cost 
implication.  Their expanding use could be counteracted with 
a higher tandem axle load to the benefit of the pavement.

ISSUE:  Tridem Axle Load Limit (spreads of 8 to 12 feet)

Advantages of a unique tridem axle limit:  Federal law is 
silent on tridem axle load limits, allowing their loads to be 
controlled by Bridge Formula B.  Bridge Formula B is: 

	W  =  500 {[LN/(n-1)] + 12N + 36}  

    where:   W = the maximum weight in pounds that can be 
                 carried on a group of two or more axles to the
                 nearest 500 pounds.  
             L = the spacing in feet between the outer axles of
                 any two or more axles.  
             N = the number of axles being considered.  

Tridem axles could be an effective means to increase truck 
load capacity while reducing pavement damage.  Combinations 
with tridem axles generally have much lower pavement cost per 
ton of freight carried than conventional combinations.  Most 
countries (including Mexico, Canada, European nations) permit 
substantially higher weights on tridems with spreads of 8 to 
10 feet (about 50,000 pounds) than is permitted in the U.S. 
by Bridge Formula B (42,000 to 43,500 pounds).

Specifying a tridem limit:  Specification of a unique weight 
limit for close-spaced tridem axles offers attractive 
technological opportunities for U.S. trucking.  There is no 
hard and fast rule for determining what particular limit 
should apply to a tridem axle relative to the limits 
specified for other axles.  From the pavement perspective, 
its specification need not be constrained by an arbitrary 
rule such as equalizing the equivalencies of single, tandem 
and tridem axle groups.  Obviously, the selected limit should 
not be so large as to overstress bridges.

Opportunities for economic benefits with tridems:  One group 
of opportunities associated with a unique tridem limit 
requires relaxing the existing 80,000-pound GVW cap to 
facilitate effective use of six-axle tractor-semitrailers.  
To illustrate the opportunities, a six-axle tractor-
semitrailer operating at a GVW of as little as 85,000 pounds 
with a tridem axle of 39,000 pounds would effect less 
pavement damage than a five-axle tractor-semitrailer at 
80,000 pounds.  Because of the increased payload capacity of 
such a unit, the pavement damage per unit payload could 
decrease even more.  Larger per unit payload benefits would 
result from an even higher GVW limit of 90,000 or more pounds 
on a six-axle tractor-semitrailer.  Both the AASHTO TS&W 
Subcommittee and the TRB Special Report 225 suggest 
consideration of the Texas Transportation Institute (TTI) 
bridge formula, which would allow up to about 90,000 pounds 
for a six-axle, semitrailer combination.  


ISSUE:  Overweight containers and Tridem Axles 

Container standards:  The International Standards 
Organization (ISO) defines the weight and dimension 
characteristics of containers used in international trade.  
The prescribed maximum dimensions are compatible with U.S. 
truck size regulations (that is, the containers fit on U.S. 
trucks).  Maximum allowable container weights are not 
compatible with U.S. truck weight regulations (that is, a 
loaded container, on a truck, can lead to the truck being 
over the Federal axle or GVW limits).

The six-axle tractor-semitrailer solution using a tridem 
axle:  An appropriate tridem axle limit within a six-axle 
tractor-semitrailer combination offers an internationally-
recognized solution to the "overweight container" problem.  
Europe specifies a unique GVW limit of 97,000 pounds for a 
six-axle semitrailer combination handling an international 
container.  Mexican and Canadian general weight limits are 
high enough to accommodate fully-loaded ISO containers.  
Canada's regulations also permit configurations which can 
handle one-20 foot and one-40 foot fully loaded containers on 
the same vehicle, or three-20 foot containers nearly fully 

ISSUE:  Tire Regulations

Varying views about need for regulating tire pressure:  
Federal and State laws are silent on truck tire pressure.  
Tire pressure has a large effect on fatigue of flexible 
pavements (albeit a small to moderate effect on rigid 
pavements).  Today's tire pressures are higher than in the 
1950s--primarily the consequence of a change from bias to 
radial ply tires.  Concern has been raised about the 
possibility of accelerated pavement rutting as a result of 
increased tire pressures.  The literature gives conflicting 
views as to whether or not pressures should be regulated:

1990	Regulation could be warranted if more pessimistic 
        analyses proved to be correct [TRB].
1993	Limit tire pressure to the recommended cold setting 
        plus 15-psi [NCHRP].
1993	More research is required to answer all questions 
        regarding relationships of tire size, contact pressure, 
        and contact area with the pavement [AASHTO].

Varying views about need for regulating tire loads:  Federal 
TS&W law is also silent on tire loads.  Many State laws 
specify some form of tire load regulation.  State regulations 
are applied to Interstate and designated highways at the 
discretion of the States.  Considerable work has explored the 
nature and extent of unbalanced loads across dual tire sets, 
among sets, and across axles.  There are conflicting views on 
whether tire loads should be regulated:

.	Many States already regulate tire loads; some do not.
.	Tire load limits have been proposed to control the damage 
        effect of wide-base tires. 
.	The effect of tire load limits or the lack of them on 
        pavement costs is unknown.


Varying views about need for regulating use of wide-base 
(super single) tires:  Federal law and most State law do not 
discourage or prohibit the use of wide-base tires.  The 
consensus of U.S. and international research is that these 
tires have substantially more adverse effects on pavements 
than dual tires.  Wide-base tires--widely used in Europe--are 
being increasingly adopted by U.S. trucking operations.  The 
benefits of wide-base tires are reduced energy use, 
emissions, tare weights, and truck operating costs.  The 
trade-off between changes in Federal pavement costs and 
operating benefits that would result from permitting or 
prohibiting extensive adoption of wide-base tires in the 
United States has not been analyzed.  The literature gives 
conflicting views as to the appropriateness of regulating 
wide-base tires:

1990	Regulation could be warranted if more pessimistic 
        analyses proved to be correct.   [TRB]
1993	Wide-base singles should be limited to loads of 650 
        pounds/inch of tread width (488 pounds/inch of tire 
        section width).  [NCHRP]  
1993	More research is required.  [AASHTO]  
1993	The relative damage potential (of wide-base tires) is 
        much less than commonly believed, and conceivably the 
        wide base tires might be less damaging than the duals. 
        [Midwest Research Institute]

ISSUE:  Road-Friendly Suspensions

Suspension system research:  Federal law is silent on 
suspension systems.  The subject of road-friendly suspensions 
(within the context of the broader subject of vehicle-
pavement interaction) is under intensive research in both the 
United States and internationally.  The work is focusing on: 
(1) how well different suspension systems can distribute load 
between axles in a group (the more evenly, the better); (2) 
how well different suspension systems dampen vertical dynamic 
loads (the more, the better), and; (3) spatial repeatability 
of dynamic loads.  Related considerations are examining how 
road and bridge characteristics act to excite a truck, and in 
turn influence the loads received by the road and bridge.

No compelling argument for suspension regulation at this 
time:  The research has yet to produce any compelling 
argument to incorporate a suspension system determinant into 
the regulations (although Mexico and some other countries 
have done so).  Whatever the case, the impacts of different 
suspension systems on pavement deterioration are of secondary 
importance compared to the static axle load levels 
themselves.  This suggests that getting the static load 
levels right first, and enforcing them second, should take 
priority over suspension system regulation.  Nonetheless, 
encouraging more use of road-friendly suspensions would be 
beneficial, particularly for large trucking operations with 
well-controlled axle loads.

ISSUE:  Lift Axles

There is little research reported in the literature on the 
extent of the use, benefits, and pavement costs associated 
with lift axles.  AASHTO and others have expressed concerns 
about enforcement problems relating to lift axles. 



The following issues are of particular interest to Federal 
policy considerations at this time: 

ISSUE:  Design Considerations behind Bridge-Related 

A fundamental on-going issue about bridges and TS&W 
regulations concerns the level of risk to accept in 
determining acceptable loadings for a given bridge or 
acceptable bridge design requirements for given loadings.  
Estimates of bridge cost impacts of TS&W changes are very 
sensitive to assumptions regarding acceptable levels of 
stress in bridges.  The inventory rating approach, used by 
some States, is considerably more restrictive than the 
operating rating approach, used by the majority of States.  

ISSUE:  Bridge Formula B

The Formula:  In addition to axle and maximum gross vehicle 
weight limits for Interstate highways in Federal law, Bridge 
Formula B, also specified by Federal law, restricts the 
maximum weight allowed on any group of consecutive axles 
based on the number of axles in the group and the distance 
from the first to the last axle.  The formula concept 
originated in the 1956 Federal-Aid highway legislation and 
was developed and presented in a 1964 report to Congress from 
the Secretary of Commerce.  Criticisms of Bridge Formula B 

1.    Bridges on Interstate highways can generally carry 
      higher weights than those allowed under the current 
      formula without being significantly overstressed.  
      However, many bridges on other highways would be 
      deficient if the maximum allowable weights for vehicles 
      on the non-Interstate highways were increased.  

2.    It is overly restrictive for shorter trucks and overly 
      permissive for short six-axle trucks and all trucks 
      with seven or more axles.  

      Views that the Bridge Formula B was overly restrictive 
      gave rise to controversy and the granting of phase-in 
      schedules upon adoption of the formula.  In those 
      States where the formula cannot be circumvented by 
      grandfather right, the formula can constrain the 
      productivity of short wheelbase vehicles such as dump 
      trucks, trash trucks and construction vehicles.  In so 
      doing, it either: (1) generates more truck movements on 
      the Interstate System than would otherwise be necessary 
      (that is, more smaller trucks handling a given quantity 
      of freight)--particularly in and around major 
      metropolitan areas (such as hauling gravel to 
      construction sites; or garbage from residential areas), 
      or (2) leads to the non-conforming heavier trucks 
      operating on lower standard highways, by-passing 
      Interstate routes.

3.    If the 80,000-pound maximum gross vehicle weight cap 
      were removed, a long nine-axle combination truck 
      carrying the allowable load would overstress HS-20 
      bridges, the typical design loading for Interstate 
      System bridges, by as much as 12 percent 


      depending on the bridge span length.  The current 
      Federal Bridge  Formula protects HS-20 bridges from 
      overstresses of  more than 5 percent.   

      State practices differ in how such overstresses should 
      be viewed.  Some States prohibit routine operation at 
      this overstress level; but in the majority of states, 
      such overstressing would not trigger posting as the 
      level of overstress is not considered high enough to 
      require it.  However, the structures could be unduly 
      damaged and their design life would most likely be 

4.    Some have found the overstress criteria--five percent 
      for HS-20 bridges and 30 percent for H-15 bridges--
      arbitrary and as having little meaning in terms of
      either consistent reliability or impact cost.  The 
      setting of these criteria considered the safety of the 
      structures for the continued, long-term use by the 
      traveling public in light of the uncertainty of bridge 
      design, construction, maintenance, and environmental 

In response to these criticisms, three recent bridge formula 
proposals have been made:

1990  TRB Study Truck Weight Limits: Issues and Options:  
      This study recommends adoption of TTI HS-20 formula 
      (developed under contract for FHWA in 1987) to be 
      applied together with existing Federal axle limits for 
      vehicles with GVWs of 80,000 pounds or less, and the 
      current bridge formula for vehicles weighing more than 
      80,000 pounds.  This increases maximum weights for 
      shorter vehicles, but leaves unchanged the maximum 
      weight for longer wheelbase trucks.

1993  AASHTO Subcommittee on Truck Size and Weight:  This 
      study recommends that AASHTO evaluate adoption of the 
      TTI bridge formula - subject to a limit on maximum 
      extreme axle spacing of 73 feet, retention of existing 
      single- and tandem-axle limits, controlling tridem 
      weights by the bridge formula, and special permitting 
      of vehicles with GVWs more than 80,000 pounds.  The TTI 
      formula generally allows slightly higher weights on 
      single units trucks and short combinations.  Applied to 
      vehicles with more than six axles, the TTI formula is 
      less permissive than the current formula.  Benefits of 
      this proposal identified by AASHTO are that it: (1) 
      gives appropriate protection for bridges with H-15 and 
      HS-20 ratings at higher weight levels and conforms 
      better to the basic bridge overstress criteria than 
      Bridge  Formula B; (2) enhances productivity by allowing 
      greater weights on short wheelbase vehicles; permitting 
      effective use of six-axle tractor semitrailer 
      combinations operating at a GVW of 89,900 pounds; 
      permitting effective use of six or seven-axle doubles 
      at a GVW of up to 98,500 pounds, with 28-foot twins; 
      (3) achieves the above without increasing pavement and 
      bridge damage, and; (4) achieves the above without 
      increasing vehicle size.  

1994  Ghosn and Moses Formula:  This formula is developed 
      from structural reliability theory.  This approach more 
      explicitly accounts for the uncertainties associated 


      bridge design and load evaluation.  The proposed 
      formula is considerably more permissive than Bridge 
      Formula B, when applied to long vehicles.  The formula 

	W = 1000(1.64 L  +  30)     for L < 50 feet

	W = 1000(0.80 L  +  72)     for L > 50 feet

		Where:  W = weight in pounds and L = distance 
       between the outer axles in the  group. 

ISSUE:  Bridges and the GVW "Cap"

The 80,000-pound GVW cap (maximum limit) is an arbitrary 
limit as the axle weight limits and bridge formula are 
designed to protect pavements and bridges respectively.  As 
such it restricts the productivity of U.S. trucks and 
highways, although some States allow heavier combinations 
under grandfather rights.  The equivalent limit in Europe is 
96,800 pounds; Canada, 137,500 pounds; and Mexico, 146,600 

However, it is important to consider such factors as design 
vehicles and criteria, structural evaluation procedures, the 
age of the existing bridges and the extent that increased 
GVWs will shorten the fatigue life of U.S. bridges must be 
included in any consideration of lifting of the 80,000-pound 

Vehicle safety issues need to be addressed as well, when 
considering higher GVW limits.  Heavier weights, for example, 
can contribute to increased rollover if steps are not taken 
to insure that the rollover potential of a vehicle is not 
increased to an unacceptable amount.  

ISSUE:  Bridges and Tridem Axles

Unique to the United States, the Bridge Formula is used as 
the method to determine the load to be permitted on a group 
of three axles connected through a common suspension system 
(a tridem).  In Europe, Canada, Mexico and most other 
jurisdictions, tridem axles are given a unique load limit in 
the same way the United States specifies unique single- and 
tandem-axle limits without direct reference to a bridge 
formula.  This is not to say that these unique tridem limits 
are not bridge-related.  In Canada, for example, the tridem 
limits prescribed by RTAC, which vary as a function of 
spacing, are based on bridge loading limitations--not 
pavement limitations.


4.2	Roadway Geometry and Traffic Operations


The following issues are of particular interest to Federal 
policy considerations at this time:

ISSUE:  Length limits of semitrailers

Federal law is a minimum specification that requires States 
to permit the operation of a semitrailer of at least 48 feet 
on the National Network (NN) for large trucks.  All States 
except Alaska and Rhode Island permit semitrailers of at 
least 53 feet on at least some highways.  Most prohibit 
longer units but eleven do permit them.  Canada and Mexico 
permit 53-foot semitrailers on national highways. 

ISSUE:  Federal maximum semitrailer length limit 

There are two reasons to consider a Federal maximum length 
limit for semitrailers: (1) to control the amount of 
offtracking in turn or a sharp curve, and (2) to standardize 
the sizes of cargo units to facilitate the intermodal 
movement of truck trailers.  Nevertheless, a Federal limit 
could stifle innovation and constrain productivity gains.  

ISSUE:  Length limits for double trailers in combination

Current regulations:  Federal law is a minimum specification 
requiring States to permit the operation of two 28-foot 
trailers in combination on the NN.  About one-fourth of the 
States prescribe 28 feet as a maximum; the others allow 
additional length with 28 and 1/2 feet being the most common. 
 Canadian regulations pertaining to A and C-train doubles 
also permit two 28 and 1/2-foot doubles.  An A-train double 
combination uses a dolly with one drawbar to connect the two 
trailers.  A C-train uses a dolly with two drawbars.  

Canadian B-trains are permitted two 31-foot trailers.  On a 
B-train the second trailer connects to the "fifth wheel" on 
an extension of the first trailer's frame.  The fifth wheel 
is the standard tractor semitrailer connection.  

Federal law permits longer doubles but does not require 
States to allow them.  Larger doubles (such as two 33-foot 
trailers) have been analyzed, as reported in TRB Special 
report 227, and demonstrate productivity advantages for cube-
out freight (given the 80,000-pound GVW cap), and weight-
out/cube-out freight (given relaxation of the cap).  

ISSUE:  Total length limits

Federal law prohibits States from specifying maximum 
combination lengths on the NN.  Most States effectively 
control total lengths on the NN, however, by limiting 
semitrailer and trailer lengths.  About two thirds of the 
States have some form of control of total 


combination length for non-NN highways; one third have none.  
Mexico and Canada prescribe maximum combination length limits.
While there are no proposals that the Federal law prescribe a 
total length limit at this time, offtracking standards would 
effectively limit overall lengths for single- and double-
trailer combinations.  

ISSUE:  Offtracking and dimensional regulations

Low-speed offtracking:  When a combination-unit vehicle makes 
a low-speed turn--for example a 90 degree turn at an 
intersection--the wheels of the rearmost trailer axle follows 
a path several feet inside the path of the tractor steer 
axle.  This is called low-speed offtracking.  Excessive low-
speed offtracking may make it necessary for the driver to 
swing wide into adjacent lanes in order to execute the turn 
(that is, to avoid climbing inside curbs or striking curbside 
fixed objects or other vehicles).  Also, when negotiating 
exit ramps, excessive offtracking can result in the truck 
tracking inboard onto the shoulder or up over inside curbs.  
This performance attribute is affected primarily by the 
tractor kingpin to center of trailer rear axle dimension, 
which is its effective wheelbase in the case of semitrailers. 
 In the case of multiple trailer combinations, the effective 
wheelbase(s) of all the trailers in the combination, along 
with the tracking characteristics of the converter dollies, 
dictate this property.  In general, longer wheelbases worsen 
low-speed offtracking.

Standard "Western" doubles (two 28-foot trailers) and triple 
combinations (three 28-foot trailers) exhibit better low 
speed offtracking performance compared to a standard tractor 
53-foot semitrailer combination.  This is because they have 
more articulation points in the vehicle combination, and use 
trailers with shorter wheelbases than semitrailers.  

High-speed offtracking:  When a combination-unit vehicle 
negotiates a large radius, high speed curve--for example at 
some interchanges between freeways--the rearmost trailer axle 
can track outside the path of the tractor steer axle.  This 
is called high-speed offtracking.  For most configurations 
that have been analytically compared in this regard, the 
amount of such offtracking is one foot or less at 55 mph.  
The effect is reduced on superelevated curves.

Current regulations:  Federal law is silent on offtracking 
related characteristics of vehicles.  In particular, it 
specifies no requirements on kingpin setting, kingpin 
setback, and rear overhang.  Nearly one half of the States 
specify a kingpin setting for semitrailers--with the most 
common value being 41 feet.  This kingpin setting effectively 
caps single trailer lengths.

Regulation alternatives:  Control of offtracking can be done 
in two ways.  The first requires considering the length 
limit(s) of the semitrailer(s) within the context of total 
combination length limit, restrictions on the kingpin 
setback, wheelbase, and effective rear overhang (per the 
Canadian regulations).  A more straightforward alternative is 
with a performance specification requiring that a truck be 
able to turn through a given angle, at a given speed, within 
a defined swept path (per the European regulations).


ISSUE:  Safe passing--passing or being passed on two-lane roads

Cars passing longer combination vehicles on two lane roads 
could need up to 8 percent longer passing sight distances, 
compared to passing existing tractor semitrailers.  Longer 
and/or heavier trucks would require incrementally longer 
passing sight distances to safely pass cars on two-lane 
roads.  In practice, safety conscious truck operators 
currently find it impractical to pass cars now in these 
situations, except under the most ideal conditions.  
Operators of longer/heavier vehicles would likely be inclined 
to follow this practice even more often.


This Section discusses current knowledge about TS&W 
considerations relating to traffic operations (capacity, 
level of service, public perceptions about flow quality, 
costs) of potential consequence to Federal policy. 

The following issues are of particular interest to Federal 
policy considerations at this time.

ISSUE:  Passenger car equivalencies, capacity, level of 
service, traffic stream costs

TS&W-sensitive passenger car equivalencies:  Traffic 
engineers use the concept of passenger car equivalencies 
(PCE) of trucks for analysis and design relating to highway 
capacity and level of service.  PCE represents the number of 
passenger cars that would consume the same percentage of a 
highway's capacity as the trucks(s) under consideration.  The 
Highway Capacity Manual (HCM) prescribes PCE values which 
vary as a function of road class, geometry, types of trucks, 
and percent trucks in the traffic stream.  The values are not 
explicitly sensitive to parameters considered in TS&W 
investigations (such as truck weight, length, configuration). 
 Recent work conducted for the American Association of 
Railroads suggests higher PCE values for certain five- or 
more-axle trucks.  This work, however, has not been subject 
to substantial peer review by traffic engineering experts.  
Microscopic simulation programs such as FRESIM could be 
calibrated to provide reasonable estimates of the PCE and 
capacity effects of a wide variety of feasible combinations 
of trucks, performance characteristics, volume:capacity 
ratios, and percent trucks as a function of grades, roadway 
section lengths, and other critical geometric conditions.

PCEs on downgrades:  Some believe that the HCM makes some 
questionable assumptions about the PCEs of trucks on 
downgrades.  Recent Canadian work identified recurring 
platooning problems behind large trucks on relatively high 
volume downgrades on two-lane primary highways in western 
Canada.  While most upgrades in such circumstances have 
climbing lanes, most downgrades have long no-passing zones.

Effects of trucks on traffic stream costs:  Changing the 
numbers and types of trucks in a traffic stream can alter the 
cost of operation of the total traffic stream.  In 
particular, changes in mean speeds, speed distributions, and 
speed changes can occur--particularly on higher 


volume routes.  All of these factors affect both vehicle 
operating costs and travel time.  Such cost effects have never
been directly evaluated in any objective manner.

ISSUE:  Trucks in merging, weaving and lane changing

TS&W considerations can have important effects on these 
maneuvers because of their effects on gap size requirements 
and acceleration performance.  Little is known about the 
effects of different percentages of trucks with variable size 
and weight on the ability to merge and change lanes in 
traffic streams of varying speed and density.  Ramp junctions 
and weaving areas are so site-specific as to their geometric 
design and operating speeds that simulation of those specific 
intersections is probably the only analytical method that 
will give reasonable precision.  

Experience with the use of longer vehicles indicates that 
skilled drivers compensate for these facts by minimizing the 
number of lane changes they make and using extra caution when 

ISSUE:  Trucks in hill climbing

As a vehicle's weight increases, its ability to climb hills 
at prevailing traffic speeds and to accelerate quickly can be 
compromised if larger engines and/or different gearing 
arrangements are not used.  When speed differentials between 
vehicles in flowing traffic streams exceed 20 mph, crash 
risks increase significantly.  On routes with steep grades, 
that are frequently travelled by trucks, special truck 
climbing lanes have been built.  However, these lanes are not 
always available, making it important that trucks be able to 
maintain reasonable performance in this regard.

In the case of multiple trailer combinations, if single drive 
axle tractors are used, a situation can arise where the 
tractor cannot generate enough tractive effort, under 
slippery road conditions, to pull the weight of the entire 
vehicle up the hill.  However, past experience has shown that 
it is unlikely that competent carriers who use routes 
susceptible to this problem, would experience repeated 
incidents of this type without taking corrective actions.

ISSUE:  Truck operations at intersections

Larger and/or heavier vehicles can affect traffic operations 
at intersections in many ways including: (1) requiring extra 
time to accelerate up to the posted speed limit; (2) altering 
sight lines; (3) increasing sight distance requirements; (4) 
altering signal timing requirements.  Many of these traffic 
disruption effects can be mitigated with the use of 
powertrains that ensure acceleration performance equivalent 
to or better than current vehicles.


ISSUE:  Trucks at terminals, ports and border crossings

Trucking activities concentrate at terminals, ports and 
border crossings, at particular times--often in or at the 
edge of seriously congested metropolitan areas.  The 
implications of TS&W changes in these areas has not been 
extensively examined.  The 1992 GAO Report on Intermodal 
Freight Transportation indicates that the success of 
intermodal trains between Chicago and the West Coast has 
increased truck traffic around Chicago's intermodal 
terminals, adding to the city's congestion.  Similar problems 
are evident in Los Angeles, New York and other port cities.  
Better understanding of the effects of change--or the lack of 
change--of Federal TS&W regulations on highly congested 
freight traffic concentration areas is needed.

ISSUE:  Public perceptions about large trucks

The literature is not extensive on the effects of TS&W 
changes on public perceptions about traffic flow quality and 
traffic impacts.  While the perception issue is not one which 
can be easily dealt with, it requires consideration in the 
evaluation of regulatory options.

European studies:  European research on public attitudes 
about trucks indicates that:

.    Medium sized goods vehicles are often preferred to either 
     fewer large goods vehicles or more small goods 
.    People think that trucks with more axles are longer than 
     they actually are.
.    People cannot detect weight differences directly, except 
     to some extent through noise level differences.

Perceptions vary by volumes and size of change:  In 
relatively high volume situations, public perceptions about 
the effects of trucks on traffic flow quality and safety are 
not positive.  While relatively small increases in vehicle 
size have gone by largely unnoticed (for example, the broad 
and rapid adoption of 53-foot semitrailers), large changes 
(for example, wide-scale adoption of turnpike doubles) would 
probably be less well-received.  Anecdotal experience in 
areas of Canada where significant changes in truck 
characteristics have occurred in response to regulation 
changes suggests that the public either did not perceive the 
changes, or did not care about them.  The relatively low 
traffic volumes of the highways most affected explains part 
of this, as does the fact that most changes took place 
without much fanfare.  

4.3	Safety


Truck accident rates have been steadily falling over the past 
10 years, more rapidly than the accident rates for passenger
vehicles.  Medium and heavy trucks accounted for 3.1 percent of
all motor vehicles in use, 3.5 percent of all motor vehicles 
involved in


crashes, and 6.8 percent of all vehicle miles travelled, in the
U.S in 1992.  The truck fleet consists of 4.3 million single 
unit straight trucks and 1.6 million combinations.  Of the 
52,227 vehicles involved in fatal crashes in 1992, 3,957 
(7.6 percent) were trucks with three of four being a 
combination.  Of the 4,462 persons killed in crashes involving 
trucks, 85 percent were occupants of cars and light trucks.  
The following issues are of particular interest to Federal 
policy considerations at this time.

ISSUE:  Data limitation problem

Accidents are relatively rare events; heavy truck accidents 
are even rarer.  But when they happen, they are seldom caused 
by a single event or factor.  Detailed information about them 
is often elusive.  It has been impossible to reach any firm 
conclusions about the role of existing TS&W regulations in 
accidents, let alone the effects of possible future changes 
in those regulations.  The following quotations illustrate 
the difficulties with attempting to hinge decisions upon the 
availability of definitive accident data:

1941	"(I)n a field so burdened with opinions and so fraught 
       with variables it is not surprising that conclusive 
       proof is lacking as to the effects of the large or 
       heavy vehicle on safety.  When the problem is further 
       narrowed to the possible effects of changes ... the 
       difficulties of analysis mount up".

1968	"(T)he analysis of ... highway traffic accidents offers 
       practically no help in determining what effects on 
       highway safety would result from increasing the limits 
       of dimensions and weight of motor vehicles ... (U)ntil 
       accident analyses can be afforded a better factual 
       basis, judgement must rest upon logical reasoning from 
       meager facts".

1981	"(T)he data that can be used to address this issue (of 
       the ... impacts of changes in TS&W on safety) are 

1990	"(D)etermining the effects of truck weight and 
       configuration on accident rates is very difficult 
       because these rates are also highly sensitive to driver 
       and environmental factors".

1992	"(E)xisting studies ... have reached widely different 
       conclusions concerning the safety of LCVs ... 
       weaknesses in the data used and different study 
       approaches contributed to the different results ... 
       thus, the safety of LCVs is largely unknown".

1994	"(I)t is unlikely that statistical analysis would be 
       able to detect statistically significant differences in 
       the safety performance of A versus C-trains".

Commentary:  It is difficult to envision a systematic 
analysis of the on-road safety implications of any feasible 
TS&W change that would not require qualifications because of 
insufficient data and/or statistical validity.  It is 
unlikely that such analyses will be able to yield compelling, 
undisputable conclusions.


ISSUE:  Predicting the accident future from the accident past

Accident data provide retrospective insights:  Attempts are 
often made to use accident data prospectively to forecast 
future trends in accident patterns if TS&W policies are 
modified.  Doing so is problematic, primarily because the 
conditions under which crashes occurred in the past are 
likely not to be the same as future conditions.

Inability to predict the decline of truck accident rates:  
The decline in truck accident rates over the past 15 years 
occurred during a period when TS&W limits were relaxed, 
operations under grandfather rights expanded, trucking 
deregulation coupled with increased competition came to pass, 
and highway traffic volumes doubled.  However, none of these 
factors is particularly conducive to reducing accidents.  

Understanding double versus single trailer accident rates:  
Many studies have investigated the relative crash involvement 
rates of various configurations and sizes of trucks, but most 
are based on limited data.  The University of Michigan 
Transportation Research Institute, however, compared the 
safety record of double- and single-trailer operations, 
controlling for differences in the time of day and roadway 
types under which the two kinds of vehicles operated.  They 
found that doubles have a slightly higher (5 to 10 percent) 
crash involvement rate than singles.  The probable reason 
cited for this difference is that doubles have been shown, on 
the basis of engineering tests, to have a slightly higher 
rollover and jackknifing propensity than singles.  

Predicting accidents involving LCVs:  There have been many 
attempts to forecast LCV accident frequencies and patterns if 
their use were expanded.  Because the extent of LCV use has 
been limited, very little historical crash data are 
available.  Further, a statistically reliable data set could 
not be assembled even with a large resource commitment.  Most 
statistics are derived from motor carrier files and primarily 
reflect experience in the West.  These data generally show 
LCVs to be safe.  This is attributable to a number of factors 
that could change including strict control on equipment 
standards, drivers, and operating conditions.  Additionally, 
the reporting carriers are typically large, well-established, 
safety-conscious fleets, operating in sparsely populated 
regions over limited access roads with light traffic 

Despite these tendencies, if fewer truck trips are made 
because of productivity gains, the number of crashes might 
not increase, assuming freight diversion from rail is not 
significantly offsetting.  Additional vehicle design changes, 
such as antilock braking systems, could offset these 

ISSUE:  Engineering for better safety

Safety equipment is available which can make the braking, 
handling, and stability performance of LCVs and other larger 
trucks equal to or somewhat better than vehicle 
configurations they might replace.  This equipment includes: 
antilock braking systems that 


control all the vehicles' axles, steerable double drawbar 
converter dollies, and suspension design and cargo body shapes 
that minimize rollover tendencies.  The Canadian Provinces have
used the approach of allowing certain TS&W changes--
particularly for vehicles with inherently advantageous safety 
performance characteristics.  These issues are further 
discussed in the next section. 


Changes in truck size and weight policies can affect the 
safety characteristics of combination vehicles because they 
precipitate changes in basic vehicle design (such as 
wheelbase, track width, center of gravity height, suspension 
properties, and axle weights).   These design changes can in 
turn affect vehicle braking, handling, stability, and 
maneuverability properties.  If these factors are degraded, 
accidents and traffic disruption can increase unless changes 
in driver performance or environmental demands counteract the 
effects of vehicle changes.  The following issues are of 
particular interest for Federal policy consideration at this 

ISSUE:  Static rollover threshold

The static rollover threshold is the level of lateral 
(sideward) acceleration that a truck can achieve during 
turning, without rolling over.  Vehicles with low rollover 
thresholds are prone to rolling over when negotiating exit 
ramps from freeways, when making severe accident avoidance 
lane change maneuvers, or when they run off road.  The 
principal determinant of rollover threshold is the ratio of 
the center of gravity height of the vehicle's mass and cargo 
to one-half the vehicle's track width.  Suspension and tire 
properties also influence this property, but to a lesser 

Rollovers account for 8 to 12 percent of all combination 
truck crashes, but are involved in approximately 60 percent 
of crashes fatal to heavy truck occupants.  They greatly 
disrupt traffic when they occur in urban environments.  

ISSUE:  Braking performance

The most straightforward measure of brake system performance 
is the distance required to stop the vehicle when fully 
loaded.  Obviously, shorter distances are considered better 
in this regard.  However, brakes must also be able to absorb 
and dissipate large amounts of kinetic energy when a fully 
loaded truck descends a grade.  Also, trucks need to be able 
to stop stably, without jackknifing or otherwise losing 
directional control due to wheels locking and skidding.  
Brake system performance could play a contributing role in 
approximately one-third of all medium/heavy truck crashes. 

The ability to stop in short distances is primarily dependent 
upon the size and number of brakes on the vehicle, their 
state of maintenance, and tire properties.  If the vehicle's 
brakes are adequately sized, which virtually all trucks are 
as a result of Federal regulatory 


requirements, they are capable of generating enough torque to 
lock most wheels on the vehicle when it is fully loaded.  
However, inadequately maintained or maladjusted brakes cannot 
generate needed braking power, which leads to longer stopping 
distances and poor brake balance.  Improper brake balance can 
cause downhill runaways and braking instability.

None of these problems are attributable to a truck's size or 
weight, they are generic truck safety issues.  However, 
because larger trucks tend to have more axles and, therefore 
brakes, to carry the heavier loads for which they are 
designed, these problems can be exacerbated if brake 
maintenance is lax.

Antilock braking systems are especially beneficial for 
heavier multiple trailer combinations because they have more 
axles/brakes which can be unevenly loaded or balanced, 
leading to incrementally increased risks of braking-induced 
instability and loss-of-control.

ISSUE:  Rearward amplification

When a multiple trailer combination is travelling at highway 
speeds (55 mph), it is susceptible to rolling over its rear 
trailer if an unexpected abrupt lane change accident 
avoidance maneuver becomes necessary.  This phenomenon 
(rearward amplification) is reduced primarily with increased 
trailer lengths and fewer articulation points.  Other design 
factors, as well as the vehicle's weight, influence this 
characteristic to a lesser degree.  Instances of these 
occurrences are rare, primarily because these type vehicles 
(doubles and triples) accumulate less than 5 percent of the 
total truck mileage and, therefore, experience comparatively 
little exposure to crash risk.  The number of incidents could 
be expected to increase, however, if larger numbers of these 
vehicles were used, particularly in denser traffic 
environments that give rise to more frequent traffic 

ISSUE:  Aerodynamic Buffeting of Adjacent Vehicles

Air turbulence around trucks does not increase if they are 
longer or heavier than currently used trucks.  However, the 
gap between the tractor and the semitrailer it tows can be 
the source of a transient disturbance to adjacent vehicles, 
if they are operating in substantial crosswinds.  Doubles 
combinations have two of these gaps, while triples have 
three.  To the extent that motorists now find these 
occurrences disconcerting, they would experience that feeling 
incrementally more often if multiple trailer combinations 
were more widely used.

Truck generated splash and spray is primarily an aerodynamic 
phenomenon. Thus the incremental concerns that arise relative 
to buffeting and multiple trailer combinations, would be 
similar relative to incremental splash and spray concerns.

Efforts to improve truck aerodynamics are continual, since 
the fuel economy benefits they can yield are substantial.  
Both buffeting and splash and spray effects will be reduced 
as these market-driven product development efforts proceed.


4.4	Permits, Pricing and Enforcement


The subject is important because (1) much trucking takes 
place under such permits and 
(2) improved permit systems with FHWA involvement have been 
proposed as a means of enhancing productivity and safety of 
trucking in a cost-responsible manner.  The following issues 
are of particular interest to Federal TS&W policy 
considerations at this time.

ISSUE:  Significant differences among State permit programs

Significant differences exist among the States in terms of 
oversize and overweight permit policies, programs, practices, 
details and fee schedules.  These differences reflect the 
needs (commodities), circumstances (geometry, traffic 
volumes), and priorities (promoting economic development) of 
the States.  They also reflect State differences in 
interpretations of the law, tolerance policies, and 
enforcement practices.  To facilitate interstate movement, 
State efforts have helped to standardize some permit 
practices at the regional level.  Recent examples include:

1994	Southern Association of State Highway and 
        Transportation Official (SASHTO): envelope vehicle of 
        length = 100 feet, height = 13.5 ft, width = 14 feet, 
        120,000 pound GVW, 20,000 pound single axle limit, 
        40,000 pound tandem axle limit, 60,000 pound limit on 3 
        or more axles
1993	Western Association of State Highway and Transportation 
        Officials (WASHTO): "Guide for Uniform Laws and 
        Regulation Governing Truck Size and Weight Among the 
        WASHTO States"

ISSUE:  Current Federal involvement in permitting

ISTEA freeze:  The ISTEA prohibits States from allowing 
expanded operation of double or triple trailer combinations 
operating at GVWs greater than 80,000 pound on the National 
Network beyond that permitted on or before June 1 1991.  FHWA 
rule-making concerning this freeze was recently completed.  
The freeze is not a long-term solution and will have to be 
reviewed before the next reauthorization.

Containers and divisible/non-divisible loads:  In 1984 FHWA 
made an administrative decision to allow states to define 
containers used in international trade as a non-divisible 
load.  In doing so, all states (and not just those ones 
having related grandfather rights) were authorized to issue 
permits for container movements at weight levels beyond that 
allowed by Federal law.  FHWA is considering a rulemaking on 
the divisibility of containers used in maritime trade.  


ISSUE:  Proposals to change Federal involvement in permitting

TRB Truck Weight Study (1990):  This study recommends that: 
(1) States be allowed to establish permit programs for 
heavier vehicles in place of States having to claim 
grandfather rights, and; (2) FHWA work with States and 
industry to establish a review and approval process for State 
permit programs.  Significant segments of the trucking 
industry have generally endorsed this proposal.  Part of this 
endorsement probably comes from a belief that this is one 
practical means by which the constraints imposed by the 
apparent entrenchment of the 80,000 pound GVW cap could be 

House Bill # H.R. 4496 (1994)--Revocation of the Symms 
Amendment:  Revocation of the Symms Amendment of the Surface 
Transportation Assistance Act of 1982 that allows States to 
define the scope of their grandfathering authority is 
proposed.  This would require FHWA to re-assume more active 
involvement in overweight permitting.

House Bill # H.R. 4496 (1994)--Extend freeze to NHS:  This 
bill proposes to extend Federal TS&W controls to the NHS, and 
to freeze permitting on that system.  This study will address 
the implications of these proposed actions.  

ISSUE:  Cost recovery and equitable truck taxes

Productivity and cost effectiveness studies performed to date 
generally indicate larger productivity benefits than negative 
or offsetting highway infrastructure cost impacts for most 
larger and/or heavier trucks.  Whether such units are to be 
authorized pursuant to a modified Federal law and/or special 
permits, their incremental infrastructure costs--and more 
specifically, recovery of these costs--are of concern to both 
Federal and State authorities.  Typically, permit fees do not 
recover the incremental costs of overweight truck operations, 
especially those under multiple-trip permits.  

The last comprehensive Federal cost allocation study was 
completed in 1982.  In concert with this TS&W study, the FHWA 
Office of Policy is undertaking an updated cost allocation 
study to determine current and projected equity of the 
Federal user fee structure.  Several States are also 
conducting similar studies. 


Because of its economic importance, most of the recent 
research has concentrated on the extent and implications of 
overweight trucking operations and enforcement strategies.  
The issues of particular interest to Federal TS&W policy 
considerations at this time are: 

ISSUE:  Lack of knowledge about non-compliance with 

Current compliance:  While many believe that there is much 
overweight trucking, the literature provides no systematic 
appreciation for the extent and nature of the problem 


(that is, what highways, vehicles, commodities, regulations 
are involved).  Nor are the implications of overweight 
trucking for pavement costs well-understood.

Effects of growth in intermodal container traffic:  Some 
believe that growth in international container traffic 
exacerbated the overweight problem because certain of the 
permitted container weights cannot be accommodated on trucks 
in the U.S. when operated pursuant to Federal TS&W 
provisions.  The Intermodal Safe Container Act of 1992 (ISCA) 
required a comparative study of truck-related overweight 
problems with container versus non-container traffic.  The 
draft report of that study (conducted for FHWA) observes that 
there is no solid evidence that container traffic is more of 
a problem than general truck traffic. 

ISSUE:  Lack of knowledge about use of multiple-trip permits 

Because of the increasing use of multiple-trip permits, the 
States are less able to determine how much use is being made 
of them.  This makes it more difficult to determine the 
appropriate cost responsibility for overweight vehicles using 
these permits.  

ISSUE:  Need for simple and reasonable regulations

Pervasive through the enforcement literature is the need for 
TS&W regulations to 
be: (1) simple to comprehend and apply, and (2) reasonable 
from the standpoint of the trucking industry and the 
enforcement community.  An overweight axle is relatively easy 
to explain in court.  Being overweight on a group of axles 
because of too short a distance between axles is not.  Add to 
this tire weight limits, and the situation becomes extremely 
complex from an enforcement perspective.  

ISSUE:  Limitations of existing enforcement techniques

Skepticism of permanent scales:  There is much skepticism 
about the effectiveness of permanent weigh scales in 
detecting overweight trucks as generally the scales are 
easily by-passed.  Portable scales are generally considered
more effective.

Some help from weigh-in-motion (WIM) and other Intelligent 
Transportation System technology:  WIM equipment can serve 
three useful enforcement purposes: (1) monitoring truck 
traffic to identify problem areas and help focus on- and off-
road enforcement efforts, (2) preclear and bypass at weigh 
scales and points of entry when used in consort with 
automatic vehicle identification equipment (AVI), and (3) 
screening trucks for portable enforcement.  WIM cannot be 
used to record evidence of violations.  Potential violators 
must be weighed at static scales to support citations.

Limited use of relevant evidence:  A few jurisdictions apply 
relevant evidence laws in TS&W enforcement.  The use of 
relevant evidence (such as bills of lading) has been 
declining in Minnesota.  Relevant evidence can only be 
applied to GVW provisions, thereby missing the most common 
and costly violations with axle weights.


Audits:  Off-road, office audits provide another means of 
assessing compliance with TS&W regulations.  Audits are more 
feasible with the larger carriers because these carriers 
generally maintain better records.  But it is these same 
carriers that are more apt to control their operations and 
their compliance.

ISSUE:  Enforceability of performance regulations

The literature is silent on how to enforce performance 
regulations.  One approach is to convert the performance 
requirements (such as a desired offtracking performance) to 
measurable surrogates (for example, kingpin setback, 
wheelbase, overhang).  This method is used to deliver the 
performance aspects of Canada's RTAC regulations.

ISSUE:  Enforceability of specially-permitted operations

Several proposals for regulation change envision special-
permitting to supplement basic specifications in the law on a 
broader scale than now exists.  The idea of these proposals 
is that State-issued and controlled special permits 
authorizing operation beyond the governing limits could be 
issued using nationally uniform guidelines to vehicles and/or 
operations considered safer and/or more road friendly.  The 
fees for such permits need to be set to recover the 
occasioned costs.  The permits would be revocable if their 
conditions are abused.  This type of permit can be much more 
self-enforcing.  It is in the carrier's and shipper's 
interests to keep the permits; revocation for non-compliance 
reasons could prove costly.  



TS&W provisions affect the types and characteristics of 
trucks permitted, the cost of operating individual trucks, 
the payloads carried by trucks, and resultant truck operating 
costs (TOCs) per unit payload.  The following factors in 
truck costs are influenced by changes in TS&W standards:

.	Vehicle dimensions (height, width, truck and trailer 
        lengths, and number of trailers)
.	Gross vehicle weight (effect of bridge formula and GVW 
.	Axle characteristics (number of axles, axle loads, 
        suspensions, and load distribution among axles in a 
.	Tire characteristics (number, type, size, tire 
        pressure, and load distribution between tires)
.	Other vehicle characteristics (type of trailer or body, 
        engine horsepower, brakes, and hitch design)
.	User fees (heavy-vehicle permit fees, graduated weight-
        distance taxes, and fuel taxes)
.	Enforcement activities (weight checks and safety 
.	Route restrictions (circuitry and access to origins and 


.	Other operational factors (availability of backhauls, 
        density  loads, availability of full loads, and speed)
.	Driver costs (pay differentials for driving certain 

Number and Length of Trailers:  Relaxation of TS&W standards 
may result in the increased use of vehicle configurations 
that are designed primarily for carrying either cube-limited 
or weight-limited freight.  Utilization rates for these 
trucks may be lower than the trucks they replace because of 
higher empty mileage, lower annual mileage, and certain 
payloads that do not take advantage of their increased 
capacity, cube or weight.  Such reduction will reduce the 
truck cost savings resulting from the increased TS&W 

If a specific TS&W standard change permitted more trailers to 
be used in selected vehicle configurations, there are costs 
related to adding the extra trailer.  These costs could 
include:  assembling and disassembling multi-trailer 
configurations, cleaning costs, the non-door-to-door 
operation, and drayage.  In general, the cost to assemble and 
disassemble twin 28-foot trailer combination is about $30 per 
trip or about 5 cents per vehicle-mile (assuming a 500 mile 
trip).  The cost to cleaning tank trailers is between $30 to 
$150, depending on the commodity.  The cost of draying the 
extra trailer ranges from $85 to $230 per trailer.  

Additional Axle:  The negative capital cost and weight 
impacts of adding an extra axle on trailers (tandem versus 
tridem axles) are about $3,000 and about 1,500 pounds of tare 

Fuel:  In general, fuel cost per vehicle mile increases by 
about 0.1 cents per mile for each 1,000-pound increase in GVW 
for a five-axle semitrailer combination with fuel costs of 
$1.25 per gallon and 5.8 miles per gallon fuel efficiency 
(Knapton, 1981).  The fuel consumption coefficients to 
measure the impact of weight vary by trailer type .

Tires:  For a five-axle semitrailer combination, tire 
consumption is estimated to be about 
3 cents per vehicle mile with a GVW of 63,000 pounds.  Tire 
costs for multi-trailer combinations are not as well 
documented at this time.  This cost is estimated to increase 
by 0.7 percent for each 1 percent increase in weight.  For a 
six-axle semitrailer combination, the extra axle is subject 
to significant tire consumption and a cost increase of about 
67 percent.  

Routes and Circuity:  Relaxation of TS&W standards on a 
limited highway system could result in some increase in 
circuity when current vehicles are replaced with larger or 
heavier vehicles.  Also, route restrictions for heavier or 
larger vehicles require less direct routing and increase 
transit times which can increase costs and decrease the 
advantage of these vehicles.  

Length of Haul:  Length of haul is relatively unimportant in 
the analyses of changing configurations or weight limits on 
transport costs.  Peat, Marwick, Stevenson & Kellogg (1993) 
found that, for cube-limited truckload shipments, reducing 
length of haul only resulted 


in changing the cost advantage of 53-foot relative to 48-foot 
semitrailer combinations from 8.4 percent to 8.1 percent.  
Length of haul does become important when comparing the costs 
of operating configurations with different numbers of trailers 
that require cleaning after each haul¾an important 
consideration for trailers used to carry chemicals or liquid 
food products.

Repair and Servicing:  The cost related to truck repair and 
servicing is affected by increased GVW.  This cost is 
estimated to change by about .097 cents per vehicle mile for 
each thousand pounds.  

In summary, there are trade-offs between changing TS&W 
standards and their costs and benefits.  For example, 
permitting or encouraging the use of an extra trailer axle 
without lifting the GVW cap increases the TOC by about 3 
percent for a typical truck load operation.  However, lifting 
the GVW cap from 80,000 to 86,500 pounds (permitted by Bridge 
Formula B) decreases the cost per payload ton-mile for six-
axle semitrailer combinations costs by about 8 percent.  

Relationship of Cost Responsibility to Total Truck Cost 

TS&W considerations can impact pavement and bridge 
consumption patterns for trucks.  Such changes can be 
measured in a traditional cost responsibility exercise.  The 
1988 Heavy Vehicle Cost Responsibility Study, concluded that: 
(1) for any configuration, the greater the weight, the lower 
the share of highway costs that are covered by user revenues; 
(2) in any weight category, the greater the number of axles, 
the higher the ratio of revenues to costs; (3) six-axle 
tractor-semitrailer and multi-unit combination vehicles with 
seven or more axles may pay a fair share of highway costs at 
weights somewhat above 80,000 pounds; and (4) twin-trailer 
combinations with nine or more axles may bear a fair share of 
highway costs at gross weights up to about 120,000 pounds, 
depending on their axle loads.  Proposed changes in TS&W 
regulations must include the analysis of cost responsibility 
and equitable payment of user fees.  Changes in user fees 
obviously affect truck operating costs.  


Generally, TS&W provisions are givens in the minds of 
logisticians, who try to optimize the movement of freight in 
the entire picture of getting commodities to market.  This 
task is getting more complex with involvement by parties not 
typically perceived in receiver/shipper decisionmaking 
process.  Some of the factors influencing change in the 
logistics environment are:

    .	Time Sensitive Delivery:  As just-in-time (JIT) 
        delivery becomes more prevalent, transit time may not 
        be as important as having accurate and reliable 
        delivery times.  Transit time is still important, 
        however, for perishable products.

    .	Inventory Costs:  Logisticians are beginning to look at 
        the cost of inventory throughout the entire productio 
        system from raw materials to finished products.


    .	Supply Chain Management:  Manufacturers are starting to 
        align themselves vertically with suppliers farther up 
        the supply chair, having each member focus on the 
        activities they do best.

    .	Global Economy:  The European Union and NAFTA are 
        removing some of the previous barriers to moving goods 
        expeditiously between countries.  

    .	Information Management Systems:  Using computer 
        systems, manufacturers are sharing production schedules 
        and sales forecasts with the other members of the 
        supply chain in order to allow them to plan production 
        and delivery better to decrease inventory and logistics 
        costs throughout the entire system.

In general, there are no laws regulating the type of 
logistics and/or distribution manufacturers and suppliers 
must use.  Since transportation cost is an inherent cost of 
delivering products to market, the free market generally 
determines the most feasible and economical forms of 
distribution and transportation.  While TS&W standards are 
factored into logistics decisions, in general TS&W 
regulations will not have a direct impact on the global 
distribution patterns of manufacturers.  

High-Value, Time Sensitive Products

The major focus for high-value, time sensitive commodities 
has been reducing inventory and transportation costs through 
integrated production planning between manufacturers and the 
entire supply chain.  This has led to a trend of smaller 
shipment sizes and more frequent deliveries, which tends to 
increase transport costs (Whitford, 1987 ).  With 
transportation costs comprising a relatively small portion of 
total product costs, the incentive to reduce inventory 
generally surpasses the cost savings associated with 
increased productivity from bigger, heavier trucks.

No literature was available that directly relates the TS&W 
issues with shipper decisions on size of shipments.  Some 
modeling work has been done on optimal shipment size that 
incorporates transportation costs.  However, many models 
treat transport costs as a single cost regardless of shipment 
size, and all assume no uncertainty in transportation.  

Truck-Load Shipment (TL) of Low-Value, Non-Time-Sensitive 

For TL shipments there is potential for benefit from longer 
and bigger trucks.  A study for FHWA found that "... an 
excellent indicator of whether or not a truckload shipper 

Whitford, R,K., "Aspect of Freight Service qualit for Just-in-
time Transportation Serving the U.S. Automobile Industry,"
Presented at "Just-in-Time Transport: New Road Freight 
Transport Strategies and Management: Adapting to the New 
Requirements of Transport Services," research Seminar, 
June 22-24,1987,Gothenburg, Sweden.


benefit from switching to LCVs is the ratio of the 
shipper's current annual single trailer freight costs to 
annual inventory carrying costs" .  This study suggests that 
single trailer freight costs are two or more times greater 
than the inventory carrying costs, therefore, switching from 
single trailers to LCVs will in all likelihood greatly reduce 
the shipper's annual total logistics costs.  This scenario 
would also apply to the terminal-to-terminal leg of LTL 
carriers as well.

While no quantifiable research has been found, there is 
definitely a relationship between products that would benefit 
from increased truck size and weight and the product's value 
and transportation costs.  For relatively low-value items and 
many regional products like coal, grain, and many petroleum 
products, transportation costs are a significant portion of 
total costs.  Thus, these products are more likely to benefit 
from scenarios that would reduce transportation costs since 
the added inventory carrying costs would likely be small.

ISSUE:   How Shippers react to Federal And State TS&W 
         limitations and resultant  benefits

Within the logistics community, those most concerned about 
the Federal and State TS&W limitations will be the carrier 
industry.  Shippers are most concerned about optimizing their 
shipments to reduce total costs¾balancing inventory carrying 
costs against transportation costs.  The shippers most likely 
to benefit from changes in the TS&W regulations will be those 
shipping goods that are low-value and non-time-sensitive 
where the transportation costs makes up a significant portion 
of the total final product cost.

Carriers, however, will be more likely to take advantage of 
the changes in TS&W limitations.  LTL carriers would likely 
take advantage of bigger and/or longer trucks on the TL 
portion of their shipments between terminals, while TL 
carriers would use the most economic configuration available 
to move the desired freight with the least amount of cost. 

The TRB Study, "Truck Weight Limit: Issues and Options" 
examined seven TS&W policy scenarios: (1) Grandfather Clause 
Elimination, (2) Uncapped Formula B, (3) NTWAC Proposal, (4) 
Canadian Interprovincial Limits, (5) TTI HS-20 Bridge 
Formula, (6) Uncapped TTI HS-20 Bridge Formula, and (7) 
Combined TTI HS-20/Formula B.  Among the impacts evaluated 
were changes in total logistics costs, which primarily 
includes transportation and inventory carrying costs.  The 
total logistics costs estimates ranged from additional costs 
to shippers of $7.76 billion for the Grandfather Elimination 
Clause Scenario to a savings to shippers of $11.69 billion 
for the Canadian Interprovincial Limits Scenario.   The 
median value was a savings to shippers of $5.11 billion for 
the Uncapped TTI HS-20 Bridge Formula Scenario.  


Use of Containers in International Trade

Although having origins in the maritime trade, the use of 
containers continues to expand in international trade, and 
more recently in domestic commerce.  While overall growth in 
intermodal traffic on railroads has been double digit, no 
attempt has been made to bifurcate that statistic into its 
domestic and international components as this can no longer 
be made on equipment type alone.

Sizes of intermodal containers moving in maritime trade 
continue to focus on 20 and 40-foot lengths as dictated by 
the design of vessels in the world cellular containership 
fleet.  Where carriers deviate, a notable example being 
American President Lines' (APL) use of 45, 48, and 53-foot 
units, utilization is limited to specific high-density trade 
lanes.  Moreover, many, if not most, foreign port and highway 
infrastructures impose their own limitations with a notable 
example being the exclusion of many high cube units from the 
European trades because of bridge and tunnel clearances.  
International trade has been growing at some multiple to the 
growth of gross domestic product (GDP), thereby suggesting 
the presence of a disproportionately larger number of 
containers on future highways. 

Historically, international containers have moved as TOFC 
(trailer or container with chassis on flatcar), COFC 
(container without chassis on flatcar), and double stack.  
Most railroad equipment has been configured for 20 and 40-
foot containers and 45-foot trailers, although newer 
equipment is providing for longer vehicles.  

ISSUE:     Impacts of Heavy International Containers

A container used in international trade, often loaded to 
gross weights up to that allowed by the International 
Standards Organization (ISO), may cause axle weight 
violations if loaded onto a tractor-chassis combination that 
has single axles rather than tandem axles; bridge formula 
violations if carried on a chassis too short for its weight; 
and, in cases, gross weight violations.  A 20-foot container 
loaded to the ISO weight limit of 24 metric tonnes on a five-
axle semitrailer requires a minimum of 36 feet between the 
first drive axle and last tag axle to comply with the U.S. 
Federal bridge formula.  A 20-foot container loaded to the 
old ISO weight limit of 20 metric tonnes on a five-axle 
semitrailer requires a minimum of 23 feet between the first 
drive axle and last tag axle.  A 40-foot container loaded to 
the ISO weight limit of 30.48 metric tonnes is too heavy 
under the U.S. 80,000-pound (36.287 metric tonnes) gross 
vehicle weight limit.  However some States, port States in 
particular, may issue overweight permits if they find that 
sealed containers are loads that cannot be easily divided. 

The fact that many international shippers are unfamiliar with 
U.S. weight limits results in many containers being loaded to 
heavily to ensure compliance with the U.S. limits.  This 
results in an enforcement problem, although probably no worse 
than overweight trucks in 

Young, R., Penn State University


general.  Many factors contribute to the use of illegally 
overweight container-carrying combinations.  Such factors 

1. 	The international nature of much intermodal 

2. 	Tight competition among ports for international trade; 

3. 	The use of per-container shipping charges; 

4. 	The competitive nature of the freight industry; 

5. 	Limited exposure to enforcement because of the 
        shortness of pick-up or delivery trips;

6. 	Uncertainty on the part of motor carriers as to how the 
        distribution of container weight will affect axle 
        loading or compliance with the bridge formula.

The Intermodal Safe Container Transportation Act of 1992 was 
enacted to address this problem.  It requires prior written 
notification and certification of the gross cargo weight 
and a reasonable description contents by the person tendering 
a loaded container or trailer having a gross cargo weight 
over 10,000 pounds.  The Act stipulates that such 
be passed to subsequent carriers of the container or trailer, 
and makes it unlawful to transport such a container or 
trailer without certification, or to coerce a motor carrier 
to move a container or trailer without certification or with 
a weight in excess of that permitted by State law.  

Section 3 of the Act required the Secretary of Transportation 
to report to the Congress on the results of a study on data 
collection and recommendations for improving the collection 
of data related to movements of containers in violation of 
the Act.  

Use of Containers in Domestic Commerce

Originally proposed as a means of utilizing empty APL 
containers needing to move from east to west coast ports, the 
addition of double stack technology suggested that real 
economies were also present for domestic commerce.  The most 
significant development has been within the past 2 to 3 years 
with the adoption of 53-foot container/chassis combinations 
by both 
J.B. Hunt and Schneider National.  

The advent of 28-foot containers for potential adoption by 
the LTL carriers is also noteworthy.  Pairs of 28-foot 
containers, as well as single 48 and 53-foot containers, are 
most easily accommodated as upper tiers on double stack 
railcars, although longer well units are being introduced.  

Domestic ISO bulk liquid containers, first introduced for 
maritime use, now show some growth potential for domestic 
commerce.  Union Pacific, as well as bulk haulers Matlack and


Chemical Leaman, continue to participate.  Equipment is 
identical to its international analog with 20-foot lengths 
being standard.


TS&W provisions affect truck travel (vehicle miles of travel-
-VMT) as well as the split of traffic between modes and use 
of intermodalism.  TS&W regulations influence payload size 
and weight, truck and trailer usage, truck costs by truck 
configuration, and other truck operating factors that affect 
the decision-making of traffic managers and carriers when 
deciding how and how much freight to carry.  

Table 1 presents the distribution of truck VMT by commodity 
and truck and trailer type for selected commodities.  The 
commodities presented were selected to give a representative 
sample of high- and low-value, bulk and non-bulk, and time-
sensitive and non-time-sensitive products.  The VMT is broken 
down by trailer type: van, refrigeration, flat bed, and 

Table 1.  Distribution of Truck VMT by Selected Commodities

Click HERE for graphic.


Impacts of Federal TS&W Law on Truck Travel

Increases in TS&W provisions will result in larger payloads 
especially for bulk commodities such as construction 
materials, agricultural and forestry products, and natural 
resources such 
as coal and potash.  The effect is not nearly as great on 
finished goods.  Increased payloads reduce the number of 
trucks required to transport a given amount of freight.  This 
reduces the amount of truck VMT.  

However, larger trucks are subject to more operational 
restrictions particularly on lower types of roadways.  
Heavier trucks may have to use circuitous routes to get 
around posted bridges.  These effects increase truck mileage 
or VMT as well as costs.  

For those commodities for which truck payloads can be 
increased, typically the TOCs per unit of payload decrease 
even with an overall cost increase.  This effect will 
increase the demand for transporting freight by truck.  Some 
of this increase may be new demand, but most of it would be 
from another mode.  Consequently, truck VMT will increase.  

The net effect of increases in TS&W limits on the truck 
travel for truck-rail competitive commodities is not well 
understood.  Most past studies have found that the net effect 
will be a decrease in truck VMT, but the lack of 
understanding of the factors considered in a shipper's choice 
between competing modes reduces the confidence in the results 
of those studies.  For transport markets where there is not 
competition between truck and rail, such as relatively short 
hauls of bulk commodities, the impacts of TS&W changes on 
truck VMT can be made with confidence.  

ISSUE:   TS&W changes can have significant impact on shipper 
         choice of mode

Past TS&W analyses provide information to group general 
trends with regard to rail market share, truck costs, truck 
VMT, and overall shipper costs.  Note, that recent TS&W 
scenario analyses are very specific with regard to TS&W 
policy changes, therefore, caution is needed when 
generalizing or grouping broad TS&W policy scenarios.  

Based on the TRB truck studies, the rail market share (both 
ton-miles and revenue), particularly with respect to 
intermodal freight, transportation equipment, and bulk 
commodities moved long distances, appears to be sensitive to 
TS&W policies that would allow: 

   .	Triple 28-foot trailer combinations to have GVWs up to 
        116,000 pounds on the Interstate System with 
        appropriate access roads.
   .	Turnpike doubles, two 45- to 53-foot trailers with a 
        total of nine axles, to have GVWs up to 129,000 pounds 
        on the Interstate System.  
   .	Other LCVs.
   .	Use of Canadian weight limits:  The bridge formula 
        would be replaced by minimum axle spacings; 51,000 
        pounds would be allowed on tridem axles; and maximum 

        GVWs for several configurations would be derived from 
        the Canadian interprovincial limits.  (The U.S. Federal 
        weight limits for single and tandem axles would 

Such TS&W policy scenarios have been estimated to negatively 
impact rail ton-miles and revenue ranging between 4 to 10 
percent, depending on the specific TS&W Policy.  However, the 
most recent GAO study of LCVs addressed the limitations of 
current models for estimating such modal impacts and 
questioned assumptions that do not reflect today's intermodal 
markets and large gains in productivity made by the railroads 
in recent years (page 33, GAO/RCED-94-106).  

Configurations Benefiting from Liberalized Truck Weight

The current Federal truck weight regulations constrain the 
use of some combinations--four-axle straight trucks and six-
axle semitrailer combinations--that could be more productive 
without any increase in size, which reduces safety and 
operational concerns.  Further, they would have less of an 
impact on pavements, but they would increase bridge stresses, 
although for most bridges, these stresses would not exceed 
the overstress criteria used to establish the Federal bridge 

Four-Axle Trucks:  For States without grandfather authority, 
the bridge formula and axle weight limits typically restricts 
the GVWs of three-axle straight trucks to a range of 
51,000 to 54,000 pounds and four-axle trucks to a range of 
55,000 to 58,000 pounds, depending on the truck wheelbase.  
Further the bridge formula restricts the maximum weight on a 
tridem-axle to a range from 42,000 to 43,500 pounds for axle 
spreads of 8 feet to 
10 feet.  The TRB Special Report 225 noted in its discussion 
of the Texas TTI bridge formula that the formula would allow 
up to 65,000 pounds for a four-axle single unit truck.  

The types of trucks that would be affected by these limits 
are fuel trucks, dump trucks, transit mixers, trucks carrying 
other building and construction materials, and trash removal 
trucks.  Given the unusually heavy empty weights for these 
trucks, these limits seriously constrain their productivity. 
 Consequently, the industries that use these trucks are 
always looking for increases in truck weight limits as even 
small increases in weight mean much larger increases in 

In the 1995 DOT Appropriations Act, Maryland was given a new 
grandfather date of June 1, 1994, which allows a 70,000-
pound, four-axle dump truck to operate on its Interstate 
highways.  This change is intended ultimately to result in 
Maryland's dump truck fleet converting from 3-axle dump 
trucks operating with weight up to 65,000 pounds to four-axle 
dump trucks operating at weights up to 70,000 pounds.  The 
Maryland provision allows a lift axle in front of the two 
rear axles.  Broader application of this provision would be 
controversial as lift axles are generally found to be 
underloaded, if they are carrying any load at all.  


Six-Axle Semitrailer Combinations:  Allowing the States to 
permit the operation of 
six-axle semitrailer combinations at GVWs of up to 90,000 or 
more pounds, as discussed in Section 4.1, would make these 
combinations about 13 percent more efficient than five-axle, 
48-foot semitrailer combinations operating at 78,000 pounds. 
 With an actual GVW cap of 90,000 pounds, the 90,000-pound 
GVW becomes slightly less attainable, and a slightly smaller 
average efficiency advantage for the six-axle semitrailer 
combination results¾probably about 12 percent.  With a GVW 
cap of 94,000 pounds and a tridem limit of 50,000 pounds, an 
18 percent efficiency advantage for the six-axle semitrailer 
combination, though the above discussion suggests that, on 
average, the practical advantage for weight-limited operation 
is likely to be about 17 percent.  

The average 12 or 17 percent efficiency advantage for six-
axle semitrailer combinations suggested in the preceding 
paragraph holds for weight-limited operation on routes that 
can be served at 90,000 or 94,000 pound GVWs.  For cube-
limited operation, six-axle semitrailer combinations are 
typically about 3.5 percent more expensive than five-axle 
semitrailer combinations.  

Relative to five-axle, six-axle semitrailer combinations have 
very clear cost advantages 
(10 percent or more) for carrying weight-limited loads when 
they are allowed to operate at 90,000 or 94,000 pounds, but 
they are disadvantageous when they are limited to 
80,000 pounds or when they are carrying loads that are not 
weight-limited.  Accordingly, allowing six-axle semitrailer 
combinations to operate at 90,000 or 94,000 pounds would 
result in an eventual switch from five-axle to six-axle 
semitrailer combinations for vehicles used exclusively or 
primarily to carry weight-limited loads on routes that allow 
operation at the higher weights.  


Federal (i.e. Congress) and State policymakers can alter 
existing truck size and weight policy and thereby affect 
energy conservation and environmental quality through basic 
standards, performance, and pricing controls.  Limits on 
gross vehicle weights (GVW) and dimensions directly affect 
energy conservation and environmental quality, but they also 
indirectly affect energy and the environment as the trucking 
industry responds to these new or modified regulations.  For 
instance, modifications in existing GVW and/or dimension 
limits may result in the modal diversion of certain types of 
freight movement (that is, truck to rail or vice versa).  
This modal shift (including intermodal shipments) impacts 
energy conservation and the environment through changes in 
vehicles' fuel consumption, emissions, and noise. 


Direct Impacts 

Gross Vehicle Weight

Federal and State set GVW limits determine the amount of 
freight that can be carried by a single truck.  Increased GVW 
limits would allow more freight to be shipped in fewer 
trucks, resulting in reduced truck VMT, truck trips, which 
would lead to reduced energy consumption, vehicular 
emissions, and total vehicular noise. 

The literature is quite old, but generally agrees that 
increased GVW limits could contribute to energy conservation 
and environmental objectives.  Several studies have found 
that increased cargo weights of 50 percent can be transported 
by a single truck with less than a 10 percent increase in 
fuel consumption.  

Vehicle Dimensions

Federal and State laws set various vehicle length, width, and 
height limits that determine the amount of freight which can 
be shipped by truck.  Changes in dimension limits can affect 
the operational efficiency of trucks and thereby affect the 
energy consumption and environmental quality because of 
changes in fuel use and emissions per ton-mile shipped, but 
generally, only in limited ways.  For instance, 
liberalization of dimension limits with no corresponding GVW 
changes improves operational efficiency only for cube-
limited, or low density cargo, which fills the volume 
capacity before reaching the GVW or axle weight limits.  From 
the data available, it would appear that dimension limits 
would have a relatively minor impact on energy conservation 
and air quality objectives.

The number of axles and/or tires follows a similar logic.  As 
the number increases, the expected GVW as well as tire 
friction with the road increase, causing an increase in fuel 
consumption and emissions.  Limited data have  shown these 
hypotheses to hold true, although no specific estimates of 
differences in fuel consumption and emissions are available. 

Indirect Impacts

Modal Diversion and Intermodal Shipments

Changes in TS&W can increase or decrease the capacity of 
trucks which could affect fuel consumption and operating 
costs.  Changes in operating costs could increase/decrease 
the modal share of all freight transported by truck.  This 
can impact energy conservation and emissions due to 
differences in the energy efficiency between the modes.

The consensus in the literature is that rail is more fuel 
efficient (ton-miles/gallon) than trucking for long haul 
shipments.  However, trucking is better than rail for drayage 
operations and for shipments where rail transport would be 
highly circuitous.  Regarding emissions, in general, trucks 
emit more pollutants (pounds/ton-mile) that rail shipments.


Regarding intermodal shipments, deregulation allows greater 
cooperation between truckers, railroads, and intermodal 
carriers.  No literature discusses the energy and emissions 
impacts of multimodal freight shipments.  This is a 
significant research gap.

Vehicle Performance, Condition, and Technology Improvements

The literature is limited, but generally shows that vehicle 
performance significantly impacts trucks fuel consumption.  
One study reported a fuel savings of 10 percent from reduced 
truck speeds from 60 to 55 miles per hour (1975 DOT).  Other 
issues which could affect energy conservation, such as 
individual driver habits (acceleration/deceleration) and 
volume-to-capacity ratio have not been addressed in the 
literature.  More research is needed to answer all questions 
regarding the relationships of vehicle performance with 
energy conservation.

Federal and State laws deal extensively with vehicle 
condition from a safety perspective.  However, laws relating 
to engine condition and fuel efficiency typically apply to 
new engines and are less imposing as the engines age.  Newer 
engines are more fuel efficient, but without proper 
maintenance, engine performance and fuel efficiency 
significantly declines.  Recent Federal and State 
environmental laws set emissions and miles per gallon 
requirements for engines (not vehicle configurations), but 
the applicability of these laws vary.  The literature agrees 
that deteriorating engine condition from age and neglect 
increases emissions and reduces fuel efficiency.  However, 
this relationship has not been quantified in the research 
identified for this study.

Another aspect of vehicle condition is tires.  Federal and 
State laws are generally silent on tires.  The literature 
gives conflicting views on tire condition.  Wide-base (super 
single) tires are believed to reduce energy consumption and 
vehicular emissions.  More research is needed to determine 
the energy conservation potential of improved tire 

Fuel consumption represents an operating cost for trucks and 
there is a financial incentive to reduce fuel consumption.  
This results in technology that contributes to energy 
conservation and emissions objectives.  The literature does 
not address all recent improvements to fuel efficiency and 
emissions.  All the literature agrees that technological 
improvements in equipment and materials, such as aerodynamic 
cabs and lightweight body designs, and engine performance 
have significantly improved trucks environmental and energy 
efficiency over the last 20 years.  Also, new Intelligent 
Transportation System technology with better communication 
and information exchange can decrease energy consumption and 



This Chapter identifies knowledge gaps and research needs 
concerning TS&W options and their impacts.  There are many 
research issues identified in the working papers prepared for 
this study.  The items listed below are judged to be the most 
important to be addressed for this Comprehensive TS&W Study. 



Research the feasible range and relative merits of 
alternative unique Federal tridem axle load limits on Federal 
bridges and pavements.  Options to consider include 
42,000/43,500 pounds (Bridge Formula B), 46,200 pounds (21 
metric tonnes), 48,400 pounds (22 metric tonnes), 50,600 
pounds (23 metric tonnes), and 52,800 pounds (24 metric 
tonnes).  Consider the merits of a unique tridem limit 
relative to the increasing use of wide-spread tandem axles.

Research the feasible range and relative merits of 
alternative increased Federal tandem 
axle load limits on bridges and pavements.  Options to 
consider include 35,000 pounds, 36,000 pounds, 37,400 pounds 
(17 metric tonnes), 39,600 pounds (18 metric tonnes), and 
40,000 pounds.  Consider the merits of alternative tandem 
limits relative to the increasing use of wide-spread tandem 

Research methods and criteria that Federal law might use to 
encourage and reward the use of road-friendly equipment and 
practices respecting such matters as suspension systems, tire 
load balancing, and tire pressure control.

Research whether or not, and if so how, the Federal law 
should discourage use of wide-base tires and lift axles.


Analyze the feasible range and relative merits of alternative 
risk criteria that FHWA could use in determining bridge load 

Analyze the need for change and relative merits of 
outstanding and proposed bridge formula alternatives.  The 
analysis should consider alternative risk criteria, unique 
tridem axle loads, alternative tandem axle loads, and 
alternative GVW caps.  Vehicles of interest include:

1.	Short wheelbase four-axle straight trucks with GVWs 
        from 64,000 to 70,000 pounds

2.	Six-axle tractor semitrailers with GVWs from 90,000 to 
        97,000 pounds



Analyze the direct pavement, bridge, and safety implications 
of allowing vehicles to operate at weights above the 80,000 
pound GVW cap.  Options will include:  

1.	The effective use of six-axle tractor-semitrailer 
        combinations with GVWs ranging from 86,000 to 97,000 
        pounds in terms of transporting bulk commodities in 
        regional trade and intermodal containers in 
        international commerce.  

2.	Use of a bridge formula for multiple-trailer 
        combinations at weights above 80,000 pounds.  



Research enhanced analytical means for evaluating the effects 
of feasible TS&W options and truck volumes on traffic 
operations--including capacity, level of service, and traffic 
stream operating costs.  The impacts of trucks on downgrades 
as well as upgrades in medium to high volume-to-capacity 
ratios are of particular interest.  The enhanced capability 
should facilitate route assessment for specially-permitted 



Define the safety-related vehicle performance test 
procedures, acceptability criteria, and implementation 
approach required for Federal truck regulation. Identify 
minimum and desirable TS&W specifications and/or performance 
regulations which would ensure compliance with these criteria 
and be enforceable and research the implications of adoption 
of such regulations.

Research technological innovations that would improve the 
safety operations of commercial vehicles and evaluate 
possible incentives through higher limits, to encourage the 
purchase of those technologies.

Determine the maximum acceptable limit for off-tracking 
performance with which trucks should comply.  Define the 
minimum and desirable TS&W specifications and/or performance 
regulations which would ensure compliance with these criteria 
and be enforceable and research the implications of adoption 
of such regulations.




Research alternative technical, management, and pricing 
aspects of Federal/State special permit approaches that could 
be used to oversee trucking operations on the NHS.  These 
could supplement the basic provisions of Federal law in a way 
similar to proposal in TRB Special Report 225.  

One potentially innovative permitting scheme is to have the 
Federal and/or State Government specify criteria that 
permitted vehicles are to satisfy, and require licensed 
professionals (such as professional engineers) to assess, 
certify, and assume responsibility for whether or not given 
vehicle configurations and/or operations are in compliance 
with the requirements.  Without certification, the permit 
would not be granted.  The concept mirrors the building codes 
within which structural engineers work and assume 
professional responsibility for their designs.

Analyze the importance of exempt and specially-permitted U.S. 
trucking operations relative to Federal TS&W law to 
facilitate evaluation of the likely impacts of potential TS&W 


Reevaluate user fee equity through an updated cost allocation 
study.  Assess marginal cost pricing concepts and the extent 
to which social costs externalities, for example 
environmental concerns, should be considered in the TS&W and 
user fee analyses.  


Evaluate with the States, the effectiveness and adequacy of 
current enforcement methods.  Assess how new technologies and 
communication methods might improve enforcement 
effectiveness, both in detecting weight limit violators and 
reducing avoidance of inspection facilities.



Assess and enhance truck costing methods for evaluating 
vehicle and TS&W policy scenario options.  



Analyze the constraints that current Federal axle limits, 
bridge formula and the GVW cap place on enhancing 
productivity and logistics.  Develop a practical 
understanding of the effects of the constraints and how they 
can be changed to facilitate productivity and logistics 
opportunities for key commodity movements, traffic lanes, 
industries, regional development objectives, and 
international trade.  The research will address the full 
range of trucking activity impacted by the Federal law--
remembering that there is probably as much or more to be 
gained by enhancing the operations of local and regional 
commodity haulers (and the like) than turnpike doubles (and 
the like).

Research on-going and expected developments in domestic and 
international containers and their implications for Federal 
TS&W law.  Examples of areas of interest include: the advent 
of 28-foot domestic container for potential adoption by the 
LTL carriers; development of domestic ISO bulk liquid 
containers.  The implications of these developments for GVW 
caps, axle load distributions, and divisible/non-divisible 
load interpretations are of interest.

Analyze the opportunities foregone by the LCV freeze imposed 
by the Intermodal Surface Transportation Assistance Act.  



Analyze the fleet mix effects of adjustments to Federal law 
that would permit the effective use of truck, single-trailer, 
and multi-trailer combinations.  


Analyze the rail to truck mode share effects of adjustments 
to Federal TS&W law such as permitting the effective use of 
rail competitive configurations.  

Develop improved methods for estimating mode shares.  


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