Comprehensive Truck Size and Weight Study
COMPREHENSIVE TRUCK SIZE AND WEIGHT STUDY
Summary Report
for
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
EXECUTIVE SUMMARY
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
mileage.
. 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
enforceability.
. Consideration should be given to the enforceability of
policy options. Enforcement of the existing relatively
simple regulations has proven difficult for many
jurisdictions.
. Developments in domestic containerization will effect
new demands on TS&W limits. The intermodal
implications of TS&W policy options also need further
study.
. 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
(NAFTA).
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
CHAPTER 1 - INTRODUCTION
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:
Safety
Pavement and bridge wear
Roadway geometry
Traffic operations
Truck operating costs
Shipper logistics costs
Truck travel
Mode share
Enforcement
Environment
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
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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.
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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
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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
involvement.
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).
5
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
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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
highways".
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
TS&W
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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.
AASHTO
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
recommendations:
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
Principles.
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
wide-
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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
interaction.
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
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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.
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CHAPTER 2 - CURRENT TS&W LAW AND 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.
11
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
combination
- 28 feet (minimum) for trailers in a twin-trailer
combination
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
12
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
stability.
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
off-tracking)
- 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
combinations
- 102.7-foot overall vehicle length limit for double
cargo unit combinations
- Minimum interaxle spacings (to control bridge loadings)
13
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
except
Mich.
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
15
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
externalities.
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
16
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
standards.
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
exists."
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
17
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.
18
CHAPTER 4 - CURRENT KNOWLEDGE OF POLICY ISSUES
4.1 Pavement and Bridges
PAVEMENT ISSUES
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
19
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.
20
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
loaded.
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.
21
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.
22
BRIDGE ISSUES
The following issues are of particular interest to Federal
policy considerations at this time:
ISSUE: Design Considerations behind Bridge-Related
Regulations
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
are:
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
23
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
reduced.
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
variables.
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
with
24
bridge design and load evaluation. The proposed
formula is considerably more permissive than Bridge
Formula B, when applied to long vehicles. The formula
is:
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
pounds.
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
cap.
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.
25
4.2 Roadway Geometry and Traffic Operations
ROADWAY GEOMETRY ISSUES
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
26
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
and
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).
27
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.
TRAFFIC OPERATIONS
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
28
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
merging.
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.
29
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
vehicles.
. 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 ACCIDENTS
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
30
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
inconclusive".
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.
31
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
densities.
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
tendencies.
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
32
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.
VEHICLE STABILITY AND CONTROL
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
time.
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
degree.
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
33
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
conflicts.
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.
34
4.4 Permits, Pricing and Enforcement
PERMITS AND PRICING
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.
35
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
circumvented.
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.
ENFORCEMENT
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
regulations
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
36
(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.
37
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.
4.5 TRUCK COSTS AND LOGISTICS
TRUCK COSTS
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
cap)
. Axle characteristics (number of axles, axle loads,
suspensions, and load distribution among axles in a
group)
. 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
inspections)
. Route restrictions (circuitry and access to origins and
destinations)
38
. Other operational factors (availability of backhauls,
density loads, availability of full loads, and speed)
. Driver costs (pay differentials for driving certain
configurations).
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
standards.
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
weight.
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
39
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 haulžan 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.
LOGISTICS
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.
40
. 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
Products
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
would
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.
41
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 costsžbalancing 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.
42
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
43
general. Many factors contribute to the use of illegally
overweight container-carrying combinations. Such factors
include:
1. The international nature of much intermodal
transportation;
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 su
