Evaluating Traffic Impact Studies - A Recommended Practice for Michigan Communitites
Click HERE for graphic.
Evaluating Traffic Impact Studies
A Handbook That Outlines:
- When Traffic Impact Studies Should Be Required
- What Analyses Should Be Included
- How The Study Should Be Reviewed And Used
- Who Is Qualified To Prepare And Review Impact Studies
Sponsored By:
- Tri-County Regional Planning Commission 913 W. Holmes Suite
201 Lansing, Michigan 48910 (517) 393-0342
- Michigan Department of Transportation
Planning Division 425 W. Ottawa P.O.Box 30050
Lansing, MI 48909 (517) 373-2240
- Southeast Michigan Council of Governments 660 Plaza Drive
Suite 1900 Detroit, Michigan 48226 (313) 961-4266
Prepared By:
- McKenna Associates, Inc.
- The WBDC Group
- With assistance from: Foster, Swift, Collins and Smith, P.C.
Francine Cullari, Attorney at Law John Aldridge & Associates
- 1994 -
Evaluating Evaluating Traffic Impact Studies
Traffic 1st Edition Published in 1994
Impact Printed by the Michigan Department of Transportation
Studies
For additional copies of this handbook contact:
Tri-County Regional Planning Commission
913 West Holmes
Suite 201
Lansing, Michigan 48910
Phone: (517) 393-0342
Fax: (517) 393-4424
Comments: This edition was prepared using data and sources
available at the time the document was developed. Users of this
handbook are encouraged to submit written comments which may assist
in revising future editions. Comments should be sent to the Tri-
County Regional Planning Commission at the above address.
Training: A training presentation on using this handbook is
available through a number of organizations. If you have a group
which may be interested, contact the Tri-County Regional Planning
Commission.
This document was prepared for the Tri-County Regional Planning
Commission in cooperation with the Michigan Department of
Transportation and the Southeast Michigan Council of Governments
(SEMCOG). Preparation of this document was financed, in part, by
funds from the United States Department of Transportation and the
Michigan Department of Transportation. The opinions and
recommendations expressed in this handbook are those of the authors
with input from committee members, and not necessarily those of the
United States or Michigan Departments of Transportation.
The Tri-County Regional Planning Commission is an Equal
Opportunity/Affirmative Action Employer. Hiring and service to
program recipients is done without regard to race, color, religion,
national origin, sex, age or handicap.
EVALUATING
TRAFFIC
IMPACT
STUDIES
A Guide for
- when to require traffic impact studies
- how to evaluate and use traffic studies
ACKNOWLEDGEMENTS
This Handbook for Evaluating Traffic Impact Studies and Site Access
was prepared for the Tri-County Regional Planning Commission, the
Metropolitan Planning Organization for the Lansing area.
Preparation of the handbook was also sponsored by the Southeast
Michigan Council of Governments (SEMCOG), and the Michigan
Department of Transportation on behalf of the 15 metropolitan
transportation planning organizations and the 14 regional planning
commissions in Michigan.
A number of reference materials from communities and organizations
throughout the nation were used in developing this handbook.
Reference materials and sample ordinances are listed in a
bibliography at the end of the document.
Two committees were formed to assist in preparation of this
handbook. An Advisory Committee met several times to provide
direction, respond to identified issues and review draft materials.
The Advisory Committee was composed of representatives of numerous
organizations including the Michigan Chapters of the Institute of
Transportation Engineers (ITE), the Michigan Chapter of the
American Planning Association (APA), and the Michigan Society of
Planning Officials. The committee included practicing
transportation engineers, transportation planners, community
planners, developers, realtors, attorneys and elected officials. A
smaller Steering Committee met with the consultant team more
frequently to provide direction and make decisions on technical
issues. While all members listed below were provided with draft
copies and invited to meetings, we particularly appreciate the time
and effort of committee members noted with an asterisk (*),
representing those who attended several meetings or provided
comments on drafts. Transportation professionals from Colorado,
Florida, Illinois, Indiana, New Jersey and New Mexico also provided
suggestions.
Report Authors
Bradley K. Strader, AICP,
Senior Principal Planner
McKenna Associates, Inc.
Peter C. LaMourie, P.E.,
Traffic Engineer/Mgr. Site Division
The WBDC Group
with assistance from:
William K. Fahey, J.D.
Brian Goodenough, J.D.
Foster, Swift, Collins & Smith, P.C.
Francine Cullari, J.D.
Attorney at Law
John M.W. Aldridge
John Aldridge & Assoc.
Denver, Colorado
graphics by:
Tanya Smith
The WBDC Group
Steering Committee Members
Paul Hamilton, Project Coordinator*
Chief Planner, Tri-County
Regional Planning Commission
Jon W. Coleman, Executive Director*
Tri-County Regional Planning Commission
William C. Hartwig, Administrator*
Project & Plan Development Division
Bureau of Transp. Planning - MDOT
Michael J. Labadie, PE, Manager*
McNamee, Porter & Seeley, Inc.
(past-President, Michigan Chapter of ITE)
Mark Graham, Director, Planning Dept.*
Delta Charter Township
Kevin McCarthy, PE, Traffic Engineer*
City of Farmington Hills
Robert A. Owen, Director*
Planning & Economic Dev. Division, City of East Lansing
Paul Hershkowitz, Supervisor*
Travel Demand Analysis Section
Bureau of Transp. Planning - MDOT
Carmine Palombo, PE, Manager*
Transportation Programs
Southeast Michigan Council of Governments
Abed Itani, Traffic Engineer*
Kent County Road Commission
David Sonnenberg, PE, Traffic Engineer*
Ingham County Road Commission
Mark Fedorowicz, Planning and Service Development Manager
Capital Area Transportation Authority (CATA)
Advisory Committee Members
Rodney Arroyo, AICP*
Birchler/Arroyo, Associates, Inc.
Athena Bacalis, Attorney at Law*
Hamburg Twp. Planning Commission
James Barrett, President
Michigan Chamber of Commerce
Nancy Bates
Michigan House of Representatives
Richard Beaubien, PE
Hubbell, Roth & Clark, Inc.
Brian Blaosing
Oaldand County Road Commission
Rand D. Bowman'
South Central Michigan Planning
Council
William Bowman, Sr.
Thompson-Brown Development
Bruce Brown, President
United Development
Jeffrey H. Brown
Lewiston-Smith Realty Corporation
Frank P. Cardimen, Jr., President
Traffic Improvement Assoc. Oakland
County
John Czarnecki, Commissioner*
Ingham County Board of
Commissioners
Tappan K. Data
Goodell-Grivas, Inc.
Steve DeHaan, Executive V.P.
Michigan Association of Homebuilders
Ed DeVries
DeVries Development
Stephen Dearing, Traffic Engineer*
City of Rochester Hills
James Dunn, Legal Council
Michigan Public Transit Association
Louis Eyde
Eyde Company, Lansing
Joel Ferguson
F & S Development Co., Lansing
Sam Frankel
Frankel & Associates
Karl F. Freed, AICP, PCP*
Professional Development Officer
Michigan Chapter, American Planning
Assoc.
Jim Foulds, Community Planning
Services Lansing
Bernard Glieberman
Crosswinds Realty
George D. Goodman
Executive Director
Michigan Municipal League
Robert Grooters
Robert Grooters Development Co.
Rebecca Harvey, Planning Director*
Oshtemo Charter Township
Robert Homan
Robert Homan, Inc.
Jason Horton
Redico Development Corp.
Phil Houdek
Schostak Brothers & Co., Inc.
Frank Janca
Bay Area Developers
Gary Jonna
Jonna Companies
Lawrence Keisling, PCP, AICP
Planning Director, Troy, MI
Barry Klein
Barry Klein Real Estate
Richard M. Lewiston
Lewiston-Smith Realty Corporation
Jim Little, Director
County Road Association of Michigan
Larry LoPatin
LoPatin & Company
Lawrence Martin, Executive Director
Michigan Road Builders Association
David Merchant, Consultant*
Lansing
Richard Neller, Consultant
Lansing
Larry Nix, Planning Division Manager
WW Engineering & Science
Grand Rapids
Michael Nystrom, Executive Director
Builders Exchange of Lansing
John L. Osmer
Michigan Road Builders Association
Keith Peterson, Executive V.P.
Bldrs. Exchange of Grand Rapids &
Western MI
Theresa Petko, Director
Grand Rapids & Environs
Transportation Study
Thomas Reel
Traffic Safety Association of Michigan
Gary Roberts, Vice President*
R. A. DeMattia Go., Plymouth
Pete Rowley
Rowley Development, Inc.
Steve Skinker*
Transportation Planner
Tri-County Reg. Planning Comm.
Jerome L. Schostak
Schostak Brothers & Co., Inc.
Doug Showers
HDI Builders
Edward Swanson, President*
Edward Swanson & Associates
Robert Taubman
Taubman Company, Inc.
Kenneth H. Tsuchiyama, Director
Public Works, City of Battle Crook
Rob Walsh, Director,* Planning &
Dev. Control, Meridian Charter Twp.
Jack Welker
Michigan Association of Realtors
Helen Willis* Executive Director
Michigan Society of Planning Officials
William W. Wright, Director'
Saginaw County Metropolitan
Planning Commission
Mark Wyckoff
Planning & Zoning Center
Irvin Yackness
Builders Association of Southeast, MI
TABLE OF CONTENTS
Page
1. Background. . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. Preliminary Considerations. . . . . . . . . . . . . . . . . . . 5
- Why Are Traffic Studies Needed?
- When Should Traffic Impact Studies Be Required?
- Types of Traffic Impact Studies
- Study Area
- Horizon Year Selection
3. Traffic Impact Study Analyses . . . . . . . . . . . . . . . . .15
- Data Availability and Requirements
- Traffic Crash Analysis
- Background Traffic
- Trip Generation Sources
- Site Access and Circulation
- Evaluation of Mitigation Alternatives
- Qualifications of the Preparer and Reviewer
- Coordinated Review and Flow Chart
4. Legal Issues Related to Traffic Impact Studies. . . . . . . . .27
5. Other Techniques to Manage Traffic. . . . . . . . . . . . . . .34
APPENDICES
I. Model Traffic Impact Study Ordinance. . . . . . . . . . . . . .A2
II. Checklists and Sample Forms. . . . . . . . . . . . . . . . . A11
- Form A: Pre-application Conference Checklist
- Form B: Letter (finding) of No Significant Traffic Impact
- Form C: Letter Requesting Review of Traffic Impact
Assessment/Statement
- Checklist for Reviewing a Traffic Impact Study
- Site Plan Review Checklist for Transportation Issues
III. References. . . . . . . . . . . . . . . . . . . . . . . . . A20
- Glossary
- Level of Service Definitions
- Sample Traffic Impact Study Table of Contents
- Bibliography
- Assistance of Metropolitan Planning Organizations and Regional
Planning Commissions
LIST OF TABLES
1. Examples of Various Land Use Size Thresholds Based on Trip
Generation Characteristics . . . . . . . . . . . . . . . . . . . . 7
2. Sample Traffic Impact Study Thresholds. . . . . . . . . . . . . 8
3. Sample Requirements for Various Types of
Traffic Impact Studies . . . . . . . . . . . . . . . . . . . . . .12
Evaluating Traffic Impact Studies - Table of Contents
The question of how to address needs associated with increasing
traffic is an on-going issue in many communities throughout
Michigan. Community decision makers often are concerned with the
traffic implications of land use decisions, but are unsure how to
address them. In Michigan, responsibility to upgrade roadways in
conjunction with new development is usually considered the sole
responsibility of the road agency. Yet road agencies often lack
funding for road improvements necessary to keep pace with
development. The public is often convinced that new development
should be denied because of perceived traffic impacts. In some
cases, communities deny proposed development based on perceived
traffic impacts without having a clear understanding of how to
evaluate and mitigate traffic impacts. Sometimes the last developer
along an already congested roadway is denied. In other cases, the
developer is expected to alleviate traffic problems before they can
build.
Traffic congestion can also negatively impact businesses, such as
when traffic backups block access to a site. Developers are often
unaware of the access limitations at their site or of the access
limitations caused by their site design. Then, after locating at a
site ill prepared to accommodate the new traffic, the developers
and citizens request improvements. The improvements may take years
to implement, if they can be implemented at all.
Current Problems:
- Lack of uniform standards.
- Communities do not adequately address traffic
implications of land use plans
- Contents of studies vary. A standard practice is needed
- Community leaders lack a guide for reviewing traffic
studies
- Traffic impacts are often inappropriatelyy used as a
reason for denial
Increasing traffic congestion causes a number of problems: crashes,
economic costs due to delays, air pollution and loss of economic
vitality. As one roadway becomes congested, others may experience
problems as motorists use routes not Intended for through traffic.
CURRENT PROBLEMS
- The lack of uniform requirements and procedures for traffic
impact studies result in a number of problems in Michigan:
- There is a lack of consistency in what communities expect and
traffic impact study preparers provide.
- Some communities require traffic impact studies only after
there is a problem.
- Some communities require traffic studies for very small scale
projects which have negligible impacts on the roadway. This
unnecessarily increases the cost of development.
- Some communities allow very large scale projects, which will
seriously compromise the integrity of the roadway system, to
be developed without evaluating likely traffic impacts and
necessary mitigation.
- Community officials are often skeptical of a traffic impact
study prepared by an applicant's traffic consultant.
- The lack of uniform procedures may lead to unnecessary
analyses, costs and delays during both preparation and review.
- The lack of recommended qualifications and guidelines for
preparing traffic impact studies results in many poorly
developed,reports. Trip generation rates and trip reduction
factors, for example, are often incorrectly used. Some
communities and developers are making decisions based on poor
analyses.
- Some local governments downplay the traffic impacts of their
land use decisions. The agency with jurisdiction over the
roadways is expected to make required improvements.
- Communities often neglect to involve adjacent communities in
the review of larger projects which may also significantly
impact that community.
- The development review process is often segregated between the
community (site plan) and the road agency (access permit).
Potential mitigation measures are often identified too
This guidebook foocuses on site traffic impact studies. Other tools
to manage traffic include:
- master plans
- corridor plans
- thoroughfare plans
- access management
- mixed use development
late in the process. The segregated process can also frustrate
developers.
Most communities do not have ordinances or guidelines which can
direct applicants and assist with their decisions, so the
sophistication of a traffic impact study depends largely upon the
preparer or what the developer is willing to include.
This handbook is intended as a practical tool to assist communities
in determining when traffic impact studies should be prepared, what
the preparer should include, who is qualified to prepare such
studies, and how communities and developers should use these
studies. This handbook and model ordinance are intended for those
involved in planning and development review at the local and
regional levels including: planning commissioners, elected and
other officials, technical staff, and professionals in the planning
and development field.
Although traffic impact studies are the focus of this handbook,
they are only one of the bundle of tools available to manage
traffic within the community. Communities frequently disregard the
traffic impacts associated with long range land use planning and
the combined impacts of individual zoning decisions.
Additional traffic management tools which can be implemented on the
local level are: effective use of the Special Land Use process
through zoning, access management (driveway) standards, travel
demand management, and coordination of local land use decisions
with the long range transportation plan of the metropolitan
planning organization (MPO) or the Michigan Department of
Transportation (MDOT). Transportation network traffic assignment
models have been developed for urban areas with a population over
50,000. These models are maintained by the MPOs or MDOT. A listing
of the metropolitan planning organizations, 3-C transportation
study areas, and a map illustrating their locations is included in
Section III of the Appendix. This handbook also briefly addresses
how these additional techniques can be implemented at the local
level.
USING THE HANDBOOK
This handbook is intended to provide an overview on traffic impact
studies, particularly on when such studies should be required and
how to review them. The handbook does not explain how such studies
should be prepared. Traffic Access and Impact Studies for Site
Development, A Recommended Practice, published by the Institute of
Transportation Engineers (ITE), and other sources provide more
guidance on the preparation of traffic impact studies. Several
references are listed in Section III of the Appendix.
This handbook is intended to present uniform practices and review
procedures considered applicable to most communities.
One method to implement the recommendations of this handbook is to
adopt the Model Traffic Impact Ordinance provided in the appendix.
The recommendations and model ordinance should be used as
guidelines. Modifications may be needed to meet the specific needs
or goals of a community.
Click HERE for graphic.
HANDBOOK FORMAT
The handbook follows the sequence illustrated in the flowchart and
outlined below.
- Why are traffic studies needed? This section discusses the
benefits provided by traffic impact studies.
- When are traffic studies needed? This section describes
various thresholds for four different types or levels of
traffic impact studies. It also outlines the need for a
preapplication conference.
- What should be Included In a traffic Impact study? This
section describes the extent of data and analyses required for
the different levels of impact studies.
- Site Access and Circulation Review. This subsection describes
how to consider access alternatives when appropriate.
- Mitigation Analysis. This subsection describes how various
mitigation options should be evaluated, including
responsibility for implementation. These mitigation measures
are intended to address identified traffic problems.
- Qualifications of Preparer and Reviewer. Traffic impact
studies must be prepared by a qualified individual. This
section outlines qualifications for both preparers and
reviewers.
- How should a traffic Impact study be reviewed and used? This
subsection discusses how the community, road agency and
affected adjacent communities (if appropriate) should jointly
review the study and utilize the data.
- Appendices. The appendices include a Model Traffic Impact
Study Ordinance, sample forms and checklists, a glossary and
other pertinent information.
2. Preliminary Considerations
- When should studies be prepared
- Different types of studies
- Holding a preapplication conference
A traffic impact analysis is a specialized study which
Assesses the effects that a particular development's traffic will
have on the surrounding transportation network. A
traffic impact study will vary in range and complexity depending on
the type and size of the proposed development.
Traffic impact studies should be an essential part of the
development review process to assist developers and public agencies
in making land use decisions, such as annexations, subdivisions,
rezonings, special land uses, and other development reviews, where
the proposal may have a significant negative impact on traffic and
transportation operations. Ultimately, traffic impact studies could
be used to help evaluate if the scale of development is appropriate
for a particular site and what improvements may be necessary, on
and off the site, to provide safe and efficient access and traffic
flow.
Communities which utilize uniform requirements for traffic impact
studies in Michigan have found the process to be very beneficial.
The process provides decision making bodies with additional
information to assist in decision making. The studies help identify
roadway improvements which should be considered. Often, developers
are willing to make improvements which will improve the safety and
convenience of their site access. The traffic impact study can also
provide a basis for negotiation between a community, a developer
and the road agency regarding improvements necessary and how the
costs for these improvements should be allocated.
Evaluating Traffic Impact Studies: Legal Issues 5
Click HERE for graphic.
WHY ARE TRAFFIC IMPACT STUDIES NEEDED?
There are a number of reasons why traffic impact studies are
needed. Traffic impact studies help to:
ù forecast the traffic impacts created by new development based on
accepted practices, not perception,
ù determine improvements needed to accommodate new development,
ù assist communities in land use decisions and road agencies in the
driveway permit process,
ù more efficiently allocate limited funds,
ù meet federal Intermodal Surface Transportation Efficiency Act of
1991 (ISTEA) requirements for managing congestion,
ù relate land use decisions with traffic conditions,
evaluate the number and location of access points, evaluate
alternatives,
ù update traffic data,
ù provide input for metropolitan transportation planning efforts, and
ù identify problems which could affect a developer's decision on
pursuing a proposed project.
Click HERE for graphic.
WHEN SHOULD TRAFFIC IMPACT STUDIES BE REQUIRED?
A traffic impact study should be required in a number of different
situations. A sample ordinance using the thresholds suggested in
this chapter is included in Appendix 1.
Trip Generation Thresholds
One of the key triggers for identifying when an impact study should
be required is "trip generation." The trip generation of a proposed
development is basically the number of inbound and outbound vehicle
trips that are expected to be generated by the development during
an average day or during a peak hour. The process of using
thresholds is as follows; estimate the trip generation, compare
that generation to accepted thresholds, and then determine the type
(ff any) of traffic study needed.
Table 1 outlines the three levels of trip generation thresholds
recommended in this handbook. The table notes when these thresholds
are met for various types of development. The three traffic study
types or levels are described in the following section.
The trip generation calculation would be based on accepted source
material or new information. The most current edition of Trip
Generation should be referenced for a more complete listing of
uses. Other thresholds used by communities are also outlined in
Table 2. The type of study needed varies with the type of project
proposed, as discussed in the next section.
Evaluating Traffic Impact Studies: Legal Issues 6
TABLE 1
Examples of Land Use Size Thresholds
Based on Trip Generation Characteristics(1)(2)
Land Use 50 Pk Hr 100 Pk Hr 750 Trips
Pk Dir Pk Dir Daily
Residential:
Single Family 70 units 150 units 70 units
Apartments 115 units 245 units 120 units
Condominiums 125 units 295 units 120 units
/Townhouses
Mobile Home Park 140 units 305 units 150 units
Shopping Center 5,200 sft. 15,500 sft. 2,700 sft.
(GLA)3,4
Fast Food Restaurant
w/ drive-in (GFA) 2,6005 5,2005 1,200
Convenience Store 650 sq.ft. 1,300 sq.ft. 1,000 sft.7
w/gas (GFA)3,6 or 3 pumps or 5 pumps
Banks w/ drive-in 2,200 sft. 4,400 sft. 2,800 sft.
(GFA)
Hotel/Motel 120 rooms 250 rooms 90 rooms
General Office 22,000 sft.5 55,000 sft.5 45,000 sft.
Medical/ 18,600 sft. 37,000 sft. 26,000 sft.
Dental Office
R & D 37,000 sft. 85,000 sft. 70,000 sft.
1.5 acres 4.5 acres or 4 acres
Light Industrial 58,000 sft. 115,000 sft. 115,000 sft.
4 acres 8 acres or 11.5 acres
Manufacturing 125,000 250,000 195,000
___________________________
Notes:
1. Rates/equations used to calculate the above thresholds are
from Trip Generation, 5th Edition, 199 1, by the Institute of
Transportation Engineers. This table will likely need updating
as future editions provide additional information.
2. For example, a full traffic impact study should be completed
(100 peak hour, peak direction trips generated) if 150 or more
single family units are proposed for a site.
3. GLA = Gross Leasable Area; GFA = Gross Floor Area.
4. Several communities require a Traffic Impact Assessment for
shopping centers of 20,000 to 40,000 square foot (GLA) and a
standard traffic impact study for larger centers.
5. Using AM peak-hour rates/equations would produce a lower
threshold. However, adjacent roadway volumes are usually
higher during the PM peak hour.
6. Uses both "Service Station with Market" and "Convenience
Market with Pumps" data.
7. Uses Convenience Market (24-hour) data (ITE 851).
8. For further trip generation characteristics of the above land
uses, or of other uses not illustrated above, refer to the
latest version of Trip Generation .
Evaluating Traffic Impact Studies: Preliminary Considerations 7
TABLE 2
Sample Traffic Impact Study Thresholds
The thresholds back on Table 1 are considered appropriate for many
communities in Michigan. They are used in a number of Michigan
communities and are also the most common thresholds used in other
states. However, a community may wish to utilize its own
thresholds. A larger community with many high volume arterials, for
example, may need to consider using higher thresholds. A rural
community or small town may want to require traffic analysis of
nearby intersections for uses which may not be noticeable in a
larger community. The thresholds may need to be lower for corridors
which are already experiencing congestion. A variety of thresholds
from a wide variety of sources are listed below for Consideration.
Click HERE for graphic.
Evaluating Traffic Impact Studies: Preliminary Considerations 8
Communities should also consider traffic implications when
preparing or updating the future land use plan or revising the
overall zoning map. this involves a more generalized traffic
impact study, usually estimating traffic on an acreage basis.
Thresholds for Rezonings and Master Plan Amendment Requests
Evaluating the traffic impacts of a proposed rezoning is difficult
to determine since a rezoning usually permits any one of a number
of uses, This issue is discussed later in this chapter under "Types
of Traffic Impact Studies."
- Requests for a rezoning consistent with the community's long
range land use plan when community officials believe the
timing of the change may not be appropriate due to traffic
issues. Ideally, a future land use plan describes the timing
or situation when the land use change is deemed appropriate.
This threshold is recommended only for a rezoning which
permits uses that could generate 1 00 or more additional trips
in a peak hour, or at least 1 000 more additional trips per
day, than would be generated by the majority of the uses
permitted under current zoning (example: a zoning change from
agricultural to one which permits 120 homes). Calculation of
"trips" is explained in Chapter 3.
- Requests for a rezoning which are inconsistent with the
community master plan for a site which could generate at least
one hundred (100) directional trips during the peak hour of
the traffic generator or the peak hour on the adjacent streets
or over seven hundred fifty (750) trips in an average day.
- Proposed rezonings along a roadway that the community or
transportation agency has identified as a "critical corridor",
"congested corridor", or "safety management corridor." This
could be applied to all such rezonings or only those which
would generate additional traffic as noted in the above
paragraph.
- Proposed amendments to the future land use plan which would
recommend uses which generate higher traffic volumes.
Thresholds for site plans, plats, mobile home parks and condominium
projects
Traffic studies for site plans, plats, mobile home parks, and
condominium projects should be more detailed than those for
rezoning since the use and proposed site design are established.
Thus, even if an initial traffic study was completed for a
rezoning, a more detailed study would usually be required for a
site plan. One key issue to address is when should reuse or
expansion of an existing site require a traffic study.
The following thresholds are recommended for most cases. These
thresholds are also used in the model ordinance.
- Any proposed site plan or subdivision plan which would be
expected to generate over one hundred (1 00) directional trips
during the peak hour of the traffic generator or the peak hour
on the adjacent streets, or over seven hundred fifty (750)
trips in an average day. A less detailed study (Traffic Impact
Assessment) is recommended for projects which could generate
50-99 directional trips during a peak hour or 500-749 trips
during an average day.
Evaluating Traffic Impact Studies: Preliminary Considerations 9
Who should attend the pre-application conference?
- Applicant
- Applicant's traffic consultant
- Community Staff or other representative
- Representative of the road agency or MPO
- Representative of an adjacent community(s) where
appropriate
- A change in an approved Planned Unit Development (PUD) to a
more intense use (on a case-by-case basis).
- Any proposed development along a corridor identified in the
community master plan or long range transportation plan as a
critical, congested or safety management corridor (segments
currently or projected to experience significant congestion or
relatively high accident rates) which would be expected to
generate over fifty (50) directional trips during the peak
hour of the traffic generator or the adjacent streets, or over
five hundred (500) trips in an average day.
- For new phases or changes to a development where a traffic
study is more than two (2) years old and roadway conditions
have changed significantly (volumes increasing more than 2
percent annually).
- A change in use or expansion at an existing site where traffic
is expected to increase by at least fifty (50) directional
trips in a peak hour.
- Special land uses, conditional land uses, Planned Unit
Developments, and other uses which are required to provide a
traffic impact study in the zoning ordinance.
- Where required by the road agency to evaluate access issues.
Typically this is based on an access code, administrative
rules or policy.
PRE-APPLICATION CONFERENCE - The First Step
When a developer proposes a project in a community, a
preapplication conference is recommended. This conference will
likely be a meeting, but may be simply a telephone conversation for
an assessment-type analysis. Community staff should coordinate the
meeting/discussion as quickly as possible. The primary reason for
this conference is to discuss the type of traffic study needed and
share information which will assist the preparers A list of items
to discuss is shown below. A preapplication conference checklist is
included in the appendix (Form A).
Items to discuss, as applicable:
- Type of study needed based on general trip generation
assumptions - traffic impact assessment, traffic impact
statements, etc.
- Study area limits
- Whether the corridor is identified as a critical corridor,
congested corridor, safety management corridor etc., requiring
special analysis
- Horizon year of build-out or years for multi-phase projects
- Availability of data and any imperfections in count data due
to seasonal variations, construction detours, weather,
development grand openings, etc.
- Whether traffic crash data should be provided
- Agreement on assumptions for background data including any
approved or anticipated projects which should be included in
any evaluation
- Agreement on acceptance of count data more than 1 year old
Evaluating Traffic Impact Studies: Preliminary Considerations 10
Types of Traffic Impact Studies
- Traffic Impact Rezoning Study
- Traffic Impact Assessment
- Traffic Impact Statement
- Regional Traffic Analysis
- Trip generation sources - community-approved rate using ITE or
local data, rate used, need for Saturday evaluation, etc.
- Trip distribution methodology
- Agreement on evaluation criteria/software to be used (i.e.
Highway Capacity Manual/Highway Capacity Software, etc.)
- Committed and programmed roadway improvements
- Right-of-way needs
- Master plan issues
Local level of service standards
- Trip reduction factors
- Other special issues
TYPES OF SITE TRAFFIC IMPACT STUDIES
This handbook recommends four types of traffic studies. The
recommended elements of each type of study are shown on Table
3 on the next page.
1. Certain rezonings or proposed amendments to the community
master plan: A traffic study for a rezoning is different than
one for a specific use, such as when associated with a site
plan. A community needs to consider all of the uses which
potentially could be developed under the requested zoning
district, regardless of any specific use being proposed. A
traffic study for rezoning should compare the potential trip
generation of representative uses permitted in the requested
zoning district with representative uses permitted under
current zoning. The community staff or the planning commission
may want to identify 3-4 "typical" uses in both the current
and requested zoning district. Other options are to determine
the average traffic associated with each of the permitted uses
and take the median or average; or use the "worst case" use
(i.e., highest traffic generator). The difference in traffic
generated should be evaluated for its potential impact.
2. Traffic Impact Assessment: This type of study is recommended
for smaller scale projects which should not have a significant
impact on the overall transportation system, but will have
impacts at the site access. The analysis for this type- of
study focuses on site access points.
3. Traffic Impact Statement: This is the traditional traffic
impact study which evaluates impacts at site access points and
appropriate nearby intersections.
4. Regional Traffic Analysis: This type of study is much more
comprehensive, focusing on the impacts over a long period. In
most cases, a regional traffic analysis will need to be
prepared using a computer model which simulates daily traffic
on the transportation network. The model projects traffic
based on the expected future development pattern and roadway
network. A regional traffic analysis may involve evaluation of
a number of optional routes, including future roadways. Such a
study may also involve a number of projects being developed
separately in the same general area. A developer may seek
assistance from the municipality, MPO, or MDOT in preparing
this type of analysis.
Evaluating Traffic Impact Studies: Preliminary Considerations 11
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Evaluating Traffic Impact Studies: Preliminary Considerations 12
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STUDY AREA
One critical issue is to determine the geographic area which the
traffic impact study should analyze and particularly which
intersections to include. The determination of the study area
should consider the characteristics of the development in relation
to the amount of traffic on the roadway system. Typically, the
larger the project, the larger the study area. Generally, the study
area should include all site access points, roadway segments, and
critical intersections (unsignalized and signalized), where traffic
generated by the project may have a significant impact. The study
area should be agreed upon at the preapplication meeting or
discussion. The following can be used as guidelines.
Rezoning: The extent of the study area would be determined based on
the intensity of the potential change in use. A large rezoning to
commercial, for example, may need a large study area including
several intersections.
Traffic Impact Assessment: An assessment would be completed for
uses which generate a relatively low volume of traffic. The
evaluation typically can be isolated to just the turning movements
at all site access points.
Traffic Impact Statement: An impact statement would be
completed for uses which generate a significant amount of traffic
(such as the 100 peak hour directional trips or 750 daily trips).
The evaluation typically should include all site access points and
nearby intersections. A number of agencies require analysis of all
intersections where the projected traffic will represent at least
five percent (5%) of the intersection volume.
Regional Traffic Analysis: These are larger scale projects, such
as a large shopping center, mall, office park, industrial park, or
large mixed use development. These projects may have an impact over
a much larger geographic area. The study area will likely include a
number of road segments and intersections quite a distance from the
site. Such a study may require analysis of alternative routes or
test the impacts of future roadways and other transportation
facilities. A transportation network traffic assignment computer
model can be used to estimate the amount and distribution of site
traffic and determine the extent of the impact area.
HORIZON YEAR SELECTION
The horizon year is the date in the future for which the traffic
impacts associated with the project should be evaluated. In most
cases, the traffic study should focus on just the expected
conditions upon completion and occupancy of the development (build-
out) or at the end of each major phase of a phased
development. In addition, evaluating long range impacts may also
prove useful if traffic projection data for the street system is
available. Traffic projections may be available from the
community or metropolitan planning organization. Typically, this
type of longer range evaluation is recommended only for larger
Evaluating Traffic Impact Studies: Preliminary Considerations 13
scale projects, such as those generating 500 or more peak-hour
directional trips. However, in rare cases it may be appropriate for
projects that generate less than 500 peak-hour directional trips;
For more on horizon year recommendations, please refer to Traffic
Access and Impact Studies for Site Development, by the Institute of
Transportation Engineers, 1991, Washington, D.C.
Evaluating Traffic Impact Studies: Preliminary Considerations 14
3. TRAFFIC IMPACT STUDY ANALYSES
Upon identification of the study parameters, the actual impact
study can be developed. The study will result in the prediction of
the traffic impacts to the surrounding roadway system caused by the
proposed development and potential mitigation measures. The
following sections briefly discuss the primary steps in the
development of the impact study process which include data
collection, analysis of existing conditions, trip generation, site
trip distribution, background traffic and future conditions
analysis and mitigation identification, if appropriate. If done
correctly, these analyses will provide communities with an end
product that will help them with their decision-making process.
DATA AVAILABILITY AND REQUIREMENTS
Data collected regarding the existing traffic volumes in the study
area is a vital piece of information to ensure an accurate study.
This data must be obtained correctly since ft becomes the base
for all of the subsequent roadway conditions analysis and the end
results of the study. In some cases, the road agency or MPO
may have available data. However, since accurate count data is
critical, use of any existing data should be discussed at the
preapplication conference.
Requirements regarding the age of the data may vary. Traffic count
data used in the study should generally not be older than two years
prior to the date of report unless locally recognized data sources
indicate traffic volumes have not increased more than two percent
annually in the past three to five years. In some cases, data up to
three years old may be acceptable if the counts can be
Evaluating Traffic Impact Studies: Impact Analyses 15
brought up to present levels based upon knowledge of traffic growth
rates in the area. In other areas of rapid growth, counts should be
no older than one year.
Peak-hour counts should typically be performed between 7-9 A.M. and
4-6 P.M. on a weekday (Tuesday through Thursday) unless the type of
development or local conditions call for different data (i.e., for
some commercial projects Saturday mid-day peak-hour data may need
to be analyzed). Twenty-four hour growth rates should not be used
to update old peak-hour turning movement volumes.
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EXISTING LEVEL OF SERVICE ANALYSIS
An impact study is basically a before and after type analysis. It
is important to identify the existing traffic operation conditions
of the study area intersections and roadway segments to allow
comparison to future conditions with the proposed project in place.
The most common analyses performed to identify the intersection
operating conditions is through "Level of Service" or "capacity"
calculations. Level of Service (LoS) is simply a qualitative
measurement of how well an intersection (or roadway) operates. LoS
is defined on a scale from A-F. Generally in Michigan, the desired
Level of Service is C. Some urban areas accept D, where it may be
unrealistic to attain LoS C. The Level of Service should be based
on the methodology and procedures outlined in the most recent
edition of the Highway Capacity Manual, published by the
Transportation Research Board. An overview on Level of Service is
provided in Appendix 111.
A table illustrating the results of the existing capacity
calculations should be included in the report. Within this table,
levels of service should be shown with their corresponding delays
or reserved capacities for each of the turning movements.
TRAFFIC CRASH ANALYSIS
Some community officials desire inclusion of some type of traffic
crash (until recently, referred to as "accident") information, at
least in some cases, to aid in making a decision. Professionals
involved in preparing traffic impact studies note that the
information may be difficult and time consuming to obtain. More
importantly, in most cases new development should not be expected
to correct the existing problems that are responsible for the
crashes.
This handbook recommends that traffic crash information may be
required, particularly for sites along an identified "Safety
Management Corridor", "Congested Corridor", or at locations with
identified problems. In these cases, such information may be
helpful to minimize any additional problems through the design or
location of access points. The need for any crash data should be
addressed at the preapplication conference.
Evaluating Traffic Impact Studies: Impact Analyses 16
Background Traffic includes:
- Expected increase in through traffic
- Traffic generated by other approved developments
BACKGROUND TRAFFIC
A traffic impact study should not be prepared in a vacuum. For
projects with an opening date at least one year away, a review of
traffic increases on the roadway which are expected regardless of
the project should be included. The analysis should include
expected increases in through traffic (defined as trips with an
origin and destination outside the study area) based on either
historic trends for the roadway or analysis using a network model.
Traffic associated with other developments under construction, or
approved for construction, should also be included.
This information should be discussed at the pre-application
conference. Expected trip generation data from previously prepared
traffic studies from other developments (open, under construction,
or approved for construction) should be provided.
TRIP GENERATION: How much traffic will the development create?
One basic factor needed to evaluate site traffic impacts is an
estimate of the amount of traffic associated with the development.
The term used to describe this factor is "trip generation". A trip
is defined as "a single or one direction vehicle movement with
either the origin or destination inside a study site" (ITE
definition). A trip is a one-way movement - i.e., a project that
generates 300 trips may mean 50 inbound and 250 outbound movements
or 150 inbound and 150 outbound, etc., depending on the types of
use and the time period.
The most commonly accepted data source is the ITE Trip
Generation manual. Local data may also be appropriate in many
cases.
The estimate of trip generation is usually based on one of two
sources: 1) Trip Generation, published by the Institute of
Transportation Engineers (ITE) and 2) local data from similar uses.
Click HERE for graphic.
Trip Generation may be used in most cases. This manual is based on
hundreds of trip generation surveys nationwide for a wide range of
development types. This manual is updated as new information
becomes available. While the studies are nationwide, they are
usually considered applicable in Michigan. In some cases, local
data may be desirable, or even more accurate, particularly for uses
where the Trip Generation rate is based on a limited number of
studies. If local data is used, the data should be collected by a
transportation professional using the procedures recommended by ITE
and presented in a manner acceptable for submittal to ITE. The data
for many uses is classified as A.M. peak hour, P.M. peak hour, peak
hour of the generator, and average daily traffic. Information on
Saturdays and Sundays is provided for some uses, such as shopping
centers.
Evaluating Traffic Impact Studies: Impact Analyses 17
Recommended Trip Factors
- Residential uses - trips per dwelling unit
- Office uses - trips per gross floor area
- Retail uses trips per gross leasable floor area
- Industrial uses - trips per gross floor area or
employee
Trips per acre are usually the least accurate though they may
be beneficial when estimating traffic on a broad scale.
Trip Generation Provides data in three forms (as shown on the next
page). The average trip rate, which expresses the average number of
trips generated per dwelling unit, per square toot, per acre, per
seat, per employee or by the most applicable independent variable.
Communities should recognize that the average rate means 50% of the
sites studied exceeded the average, while 50% were below.
Therefore, rates other than the average should also be considered.
Some Michigan communities require an applicant to use a rate one
standard deviation above the average to decrease the likelihood
that traffic will be underestimated.
The trip generation data is plotted on a graph. The graph typically
includes two lines, one depicting the average rate and the other
depicting the regression equation results which best fit the data
points. The better this second line fits with the points, the more
accurate the equation. The regression line is also shown as an
equation at the bottom of the page. Many traffic professionals
recommend using the equation if the correlation coefficient (R 2)
shown on the chart is above 0.75.
Using Trip Rates
While the community officials and residents often focus on the
number of trips generated in a typical day, traffic professionals
typically focus on the peak-hour volumes, since an analysis of peak
hour conditions results in a more accurate identification of site
traffic impacts.
The number of vehicle trips generated by the site may include many
types of trips, including some traffic that is already on the
street. Traffic studies may account for these trips using
"reduction factors."
Trip Reduction Factors
Typical trip generation rates or equations are usually derived from
counts taken at driveways of various land uses. However, for many
commercial land uses, not all of the trips generated at the
driveway(s) represent new trips added to the adjacent street
system. The number of trips generated may include pass-by trips,
internal trips or transit trips.
Pass-by trips are made by traffic already on the roadway(s) that
enter the site as an intermediate stop on the way from an origin
and primary destination. For example, a driver may stop at a
convenience market on his/her way home from work. If this market is
located along the roadway the driver normally uses to get home,
then the trip "generated by the market" is not a new trip added to
the roadway system.
This trip generated does not impact nearby intersections, but does
impact traffic flow at the site entrance. It is appropriate for the
traffic impact study preparer to use this type of reduction factor
it can be documented. Since trip generation rates and equations
Evaluating Traffic Impact Studies: Impact Analyses 18
Click HERE for graphic.
Evaluating Traffic Impact Studies: Impact Analyses 19
are based upon driveway volumes, this pass-by factor should be
taken into account for many commercial land uses.
As an example, standard trip generation rates (ITE) indicate that a
300,000 square-foot shopping center would generate approximately
1,320 P.M. peak-hour trips at its driveways. Given an expected
pass-by percentage of 25 percent, the amount of additional traffic
on the adjacent roadway system would be approximately 990 trips
(1,320 x (1 - .25)). It should be noted that the full 1,320 trips
should be shown (and analyzed) at the site driveways. Pass-by
reduction is only applicable to evaluation of traffic operations at
intersections removed from the site. Appendix III contains more
information on pass-by trips including sample reduction factors for
several land uses. The use of trip reduction factors should be
discussed during the pre-application conference.
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The number of trips associated with a development may also be
reduced based on "internal trips", car and vanpooling and transit
use. Internal trips are typically used for larger mixed used
projects, Such as an office park with a restaurant. Such reduction
factors should be used cautiously and be documented.
Click HERE for graphic.
For more information and discussion regarding pass-by trips and
other potential reduction factors see ITE's Trip Generation, Fifth
Edition, 1991; or "Trip Generation Analysis - Considering Pass-by
and Internal Trips", Planning and Zoning News, March, 1989. Some
critics of pass-by calculations have noted that the R 2 values are
very low, meaning mathematically their validity is questionable.
DIRECTIONAL DISTRIBUTION AND ASSIGNMENT
Once the forecast trip generation is identified, the expected
direction of approach and departure needs to be estimated (i.e.,
the percentage of trips oriented to the north, south, east and
west). This directional distribution is most often based on counts
on adjacent roadways and nearby driveways, market study
information, other rationale associated with trip generators (i.e.,
population or employment distribution), or travel model
distribution results. A distribution or "gravity" model considers
factors such as travel time between land uses and their traffic
relationship - for
Evaluating Traffic Impact Studies: Impact Analyses 20
example the pattern of residential development around a
neighborhood shopping center. Site traffic typically is assigned to
the roadway network manually or by a network traffic assignment
model, depending upon the type of study required.
FUTURE LEVEL OF SERVICE ANALYSIS
The traffic study should show the projected levels of service (LoS)
for all movements at signalized intersections and for all critical
movements at unsignalized intersections (critical movements are all
the movements except the through movements on the major roadway).
Levels of service should also be evaluated for the critical
movements at site access points.
Click HERE for graphic.
The next step is to determine if mitigation is necessary. A
community should have a policy on the level of service which will
be accepted. If the community LoS standard is C, and the proposed
project will produce LoS E or worse at one or more movements at a
nearby intersection or site access point, mitigation needs to be
evaluated.
Some Michigan communities and road agencies have a goal that the
LoS for an intersection cannot drop more than two levels (i.e., A
to C) and must remain at D or better. If the intersection LoS is
currently E, F, or worse, some communities stipulate that the
current LoS must be maintained or improved.
Click HERE for graphic.
SITE ACCESS AND CIRCULATION REVIEW
One key element not often included in traffic impact studies in
Michigan is an evaluation of site access and internal circulation.
The ITE Traffic Access and Impact Studies for Site Development
guidebook recommends that analysis of access points be addressed in
a traffic study.
Poorly designed or poorly located access points can impact safety
and reduce the capacity of the roadway. The 1990 design policy
adopted by the American Association of State and Highway
Transportation Officials (AASHTO) considers access points to be
intersections. Access points should be designed with the same care
and consideration as intersections. However, many communities and
road agencies in Michigan lack access standards.
Access issues involve both municipal plan review and road agency
access review. A comprehensive and coordinated review
process can help avoid problems. Communities and road
agencies should also consider access codes,access management
policies or driveway design ordinances if they are lacking (see
Access Management section).
A number of access and circulation issues should be evaluated. A
site plan review checklist for traffic related issues is included
in Appendix 11. Checklist issues include:
Evaluating Traffic Impact Studies: Impact Analyses 21
Click HERE for graphic.
- Are the number of access points the minimum necessary to serve
the project without negatively impacting the flow of traffic
along arterial streets?
- Are proposed access points a sufficient distance from
intersections to minimize conflicts?
- Are proposed access points aligned with, or sufficiently
offset from, those across the street or adequately spaced from
other access points along the street?
- If a traffic signal is proposed, will it be located and timed
to facilitate traffic progression past the site?
- If there is a median, are the number, location, and design of
crossovers adequate to meet project needs without sacrificing
safety or good traffic progression?
- Should left turns, (which create the most conflict), be
restricted by signs, channelized driveways or installation of
a median?
- Have other methods of access (such as shared driveways,
frontage roads, rear service drives or access off a side
street) been evaluated?
- Is the sight distance adequate at proposed access points?
- Are changes needed to the driveway geometries, such as the
number of exit lanes, radii, deceleration lanes/tapers, etc?
- Is the throat length at the driveway sufficient to minimize
conflicts with street traffic and within the site?
- Can trucks and waste hauling vehicles easily access the site
and circulate to and from loading areas?
- Is the design sensitive to pedestrian needs?
- Will driveway radii accommodate expected vehicles (i.e.,
trucks, buses, etc.)?
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EVALUATION OF MITIGATION ALTERNATIVES
The major benefit of a traffic impact study is to determine what,
if any, mitigation measures are needed. Mitigation could involve
physical or operational improvements along the roadway and site
access points. The study should present mitigation alternatives and
recommendations. The mitigation measures should consider the
following:
- Improvements already scheduled by the road agency (for
example, constructing a by-pass lane may not be cost effective
if a roadway widening is scheduled).
- The phasing of the development.
Evaluating Traffic Impact Studies: Impact Analyses 22
- A logical phasing of improvements.
- Responsibility for approving the design and availability of
funding.
The question of whether an off-site improvement can be required as
a condition of approval should be addressed by the municipality's
attorney. Off-site mitigation identified in the traffic study could
be required, dependent upon the opinion of the municipal attorney.
Even if off-site improvements such as a left turn by-pass lane
cannot be required, there may be alternatives. For example, left
turns could be prohibited where they may create a problem unless
the developer offers mitigation. A road agency (city, village, MDOT
or road commission) has greater authority to require off-site
improvements than a municipality with only site plan review
authority. Therefore, close coordination between the municipality
and road agency can be more successful in achieving off-site
improvements funded, in part, by the developer. Regardless of off-
site mitigation, a municipality can use the findings of the impact
study to modify site design - the number and location of driveways,
for example.
Mitigation measures are not limited to roadway construction or
other physical improvements. Mitigation can include changes to
traffic signal timing, reducing the number of trips generated in
the peak hour or even denying the project if mitigation cannot be
achieved.
Click HERE for graphic.
Examples of Mitigation Measures:
Roadway Improvements
- construct a by-pass lane
- pave the roadway
- realign a street
- improve sight distance
- widen the roadway
- intersection improvements
- add deceleration/acceleration lanes
- add a traffic signal if warrants/spacing criteria are met
- add a median crossover
- construct or modify an interchange
Access Management Techniques
- increase driveway spacing from intersections
- relocate driveway(s) or intersection(s)
- reduce the number of driveways
- install a median
- develop a service road system
- share access with adjacent land
Operational Improvements
- change signal timing or phasing
- improve signal progression
Evaluating Traffic Impact Studies: Impact Analyses 23
- reduce peak-hour trips through use of transit
- off-peak shift changes, etc. (i.e., demand management)
Site Plan/Land Use Techniques
- reduce project size
- modify project phasing
- increase driveway queuing
- revise internal circulation
- revise service vehicle/truck access or circulation
- pedestrian or bicycle circulation
- use of directional signs and pavement markings
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QUALIFICATIONS
Preparer: The preparation of a thorough traffic impact study
requires extensive background and experience in traffic-related
analyses. Therefore, the experience of the preparer best defines
his or her ability to provide a technically sound analysis.
Recommended preparer requirements are outlined below,
I. The person responsible for the preparation of the study shall
meet the following requirements:
1. Three or more years of recent experience in the
preparation of traffic impact studies.
2. The development of impact studies (and similar
intersection and/or corridor analyses) comprise a major
component of the preparer's recent professional
experience. This requires ongoing experience and
familiarity with the Highway Capacity Manual techniques
as well as the computer software (Highway Capacity
software and others) that provide level of service
results and other analysis findings needed to fully
assess potential impacts.
3. Specific education, training, and/or professional
coursework in traffic impact analysis from an accredited
college or university or other professional
transportation training organization (ie. National
Highway Institute, Northwestern University Traffic
Institute, etc.).
4. The study preparer shall be an associate (or higher)
member of one or more professional transportation related
organizations, particularly the Institute o f
Transportation Engineers (ITE) or the Transportation
Research Board (TRB). This helps ensure that the preparer
is maintaining his or her knowledge as new research is
published and analysis techniques are changed or refined.
II. In addition, the preparer should have one of the following
professional qualifications:
Evaluating Traffic Impact Studies: Impact Analyses 24
1. A registered engineer (PE).
2. A community planner with AICP or PCP certification.
3. A trained professional transportation planner.
III. Any study involving roadway or traffic signal design work
shall be prepared by or under the supervision of a registered
engineer (PE) with specific training in traffic engineering.
IV. The study should include a resume of the preparer responsible
for the report. The study may also include relevant experience
of the preparer's firm. The study should also be signed by the
preparer with full recognition of potential liability for the
results and recommendations outlined in the report.
Reviewer: Review of the study is important to ensure that the
analysis and recommendations are based on accepted practices. The
ITE recommends that the traffic impact study be reviewed by
"trained traffic engineers or transportation planners." The
qualifications of the reviewers should parallel those of the
preparers as outlined above.
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COORDINATED REVIEW PROCESS
Traffic impact studies should be reviewed concurrently by staff
with jurisdiction along the roadway (road commission, MDOT,
engineering or public works department, etc.) and the planning or
zoning staff/commission. Professional transportation staff of the
local metropolitan planning organization or regional planning
agency may also be able to assist local governments and road
agencies in reviewing these studies. Lists of the names and
addresses of these organizations are included in Appendix 111. A
suggested review procedure is shown on the next page.
Using the Study
The study can provide a number of benefits to the community, road
agency and the developer:
- help make decisions on development proposals;
- determine changes needed before access permits are issued;
- indicate if the site will meet the developer's needs;
- indicate improvements which may be needed;
- suggest changes to the project plan;
- findings could be incorporated into transportation network
models or plans;
- help develop capital improvement programs;
- support funding from outside agencies; and
- indicate if the Master Plan or zoning ordinance needs to be
revised.
Evaluating Traffic Impact Studies: Impact Analyses 25
Click HERE for graphic.
Evaluating Traffic Impact Studies: Impact Analyses 26
4. LEGAL ISSUES RELATED TO TRAFFIC IMPACT STUDIES
One key issue in evaluating traffic impacts and associated 0
improvements is "Can we require the developer to fund improvements
to the roadway?" While some states use impact fees and other
techniques to "exact" funding for roadway improvements from the
developer, improvements in Michigan are typically funded by the
road agency.
The authority of Michigan municipalities to regulate land use is
limited to that authority expressly granted or necessarily implied
by state statutes. The scope of that authority generally, although
not exclusively, has been narrowly construed by Michigan courts in
regard to off-site exactions and improvements. This chapter reviews
some of the landmark Michigan cases involving transportation
improvements.
Subdivision Control Act
The earliest Michigan case to address a roadway exaction from a
developer was decided in 1928. Ridgefield Land Company City of
Detroit, 241 Mich 468, 217 NW 58 (1928). The city did not require
improvements from the developer but did require a dedication of
land for improvements planned by the city as part of a subdivision
approval.
The developer maintained that the statute authorizing the city to
approve plats, Act 360 of 1925, granted the city no power to
require the width requested, or that if the statute did confer such
Evaluating Traffic Impact Studies: Legal Issues 27
In the landmark Arrowhead v. Livingston County Road Commission
case, the court found that the law specifically provides that
borrowing and taxation are the methods for financing road
improvements and there is no authorization for any other means
of acquiring funds. The court found that exacting the cost of
improvements to county roads outside a subdivision from the
developer cannot be fairly implied from the County Road Law.
power, it was a constitutional infringement which required the
dedication of private property for public use without compensation.
The court found no merit to the contention. It stated that:
"the streets ... are too narrow for present traffic
conditions. It has become necessary for the general
convenience and the public safety to widen them, and to
prevent others of the same kind from being established.
Because of this necessity, there is nothing unreasonable in
the demand of the city that the streets designated ... conform
to the general street plan. It has been determined that
streets of a certain width are necessary to accommodate the
traffic. They are necessary for the public safety and
therefore, the right to provide for them is within the police
power of the city,"
The court found that the city's requirement was a proper exercise
of its power of eminent domain. Thus, the city could impose a
reasonable "voluntary" dedication of land before the subdivision is
accepted for record in return for the advantage and privilege of
having the plat recorded.
Some 50 years later, a more restrictive view was held by the
Michigan Supreme Court, when a road commission required a developer
to improve an off-site road. Arrowhead v Livingston County Road
Commission, 413 Mich 505, 322 NW2d 702 (1982). The Arrowhead
developer submitted a residential subdivision to the County Road
Commission for approval. The Commission required improvements on a
road entirely outside the subdivision where no lots were platted
along the road. The case presented two issues: (1) whether a county
road commission could require a developer under the Subdivision
Control Act to make improvements on a county road located outside
the subdivision and (2) whether the exercise of that authority is
constitutional under the takings clauses of the US and Michigan
Constitutions. The court declined to address the constitutional
issue since it decided the case by finding the County Road
Commission did not have authority under the Subdivision Act to
condition its approval upon the improvements.
The Commission relied upon Article 7 Section 34 of the Michigan
Constitution, as well as the County Road Law and the Subdivision
Control Act. Article 7 Section 34 of the Michigan Constitution
provides that the constitutional laws concerning municipalities
shall be liberally construed in favor of the municipality. Further,
Section 34 states that powers granted to counties and townships
shall include those fairly implied and not prohibited by the
constitution.
The court found that a County Road Commission draws its authority
strictly from the County Road Law which is a creation of the
legislature. Therefore, it has no power except that which is set
forth in the road law. The court was unable to find any basis in
the law to conclude that the commission could discharge its duty to
keep roads in reasonable repair by imposing the cost of its
improvements on developers of nearby subdivisions. The court found
that the law specifically provides that borrowing and
Evaluating Traffic Impact Studies: Legal Issues 28
In the Arrowhead case, the court stated that requiring a
developer to fund off-site improvements would depart from the
historic manner of funding public improvements - taxation and
special assessments.
taxation are the methods for financing road improvements and there
is no authorization for any other means of acquiring funds. The
court found that exacting the cost of a county road improvement
from a subdivision developer cannot be fairly implied from the
County Road Law.
In analyzing the Subdivision Control Act the court found that even
the most liberal construction reasonably warranted would not
justify the authority to impose the cost of a county road
improvement outside a plat. Section 183 of the Subdivision Control
Act provides that the County Road Commission may require adequate
provisions for traffic safety and laying out drives which enter
county roads and streets. The court found that the County Road
Commission can require improvements to roads shown on the plat or
roads required to be shown on a plat, but that the reference means
roads within a proposed subdivision. The court further found that
simply by publishing rules, the road commission could not expand
the authority granted to it by the legislature.
The court speculated that if it reached any other conclusion at the
intent of the legislature, its interpretation would lead to
justification of imposing the cost of police and fire protection,
traffic signals, public school facilities, public lighting, road
widening and other public services on a residential developer. The
court said these are not costs historically imposed upon the
developer, but rather are met by taxation and special assessments
to benefit individuals and property. To impose such a burden on a
nearby developer would depart from the historic manner of funding
alterations to public property. If the legislature wished to impose
such a burden, it would have made such an intention explicit, The
court did not deal with the constitutionality of requiring such a
burden, but the case can be read to suggest that if there were a
specific intention made by the legislature perhaps such an intent
would be upheld.
In Troy Campus v. City of Troy, 132 Mich App 441, 349 NW2d 177
(1984), the city denied a rezoning from residential to office along
Crooks Road, then the third most heavily travelled road in the
city. The case is frequently cited for the proposition that the
last developer to build in an area which has existing traffic
problems should not bear the burden of improvements. In fact, the
city did not require exactions from the developer, but did use
traffic impact as one reason to deny the rezoning petition. The
case was actually decided against the city on issues entirely
unrelated to exactions and improvements, and the dicta regarding
the burden for improvements, is not as broad as usually portrayed.
The court stated:
"Crooks Road is a major thoroughfare intended to carry large
volumes of commercial traffic. The problems created by the
nature of the road and of the uses served by the road are
problems created by the city in establishing this area as a
center of office and commercial activity -- they are public
Evaluating Traffic Impact Studies: Legal Issues 29
problems . The burden and cost of dealing with these problems
should be fairly distributed among the public, and should not
depend upon the fortuity of he who develops his land last.
That is, it is unreasonable to impose such a disproportionate
share of the cost of dealing with problems generated by Crooks
Road traffic on the last developer to locate along this busy
major road. See Alderton v. Saginaw, 367 Mich 28; 116 NW2d 53
(1962). (emphasis added)
The court did not discuss any authority one way or the other for
requiring exactions from a developer and did not address the
specific issue that a proportionate share of the cost might be
imposed upon each developer.
In an unusual case, CPW Investments #2 v. City of Troy, 156 Mich
App 577, 401 NW2d 864 (1986), the Court of Appeals did uphold a
city's requirement for improvements to a county road. However, in
this case the developer had shown the public road within the plat.
The court distinguished the Arrowhead case, supra, where a county
road commission required improvements to an off-site county road.
Roads which are shown or required to be shown and upon which
improvements can be required, are those "within the parcel or tract
of land in which the proprietor has an ownership interest, which is
the area actually to be divided or partitioned." The court found it
inequitable to allow the developer to provide funds for an
improvement, then reap the economic benefits with increased lot
values, and expect a refund from the city after selling all the
lots.
A recent case upheld a township requirement that a developer
construct an access road on land outside a proposed subdivision.
Altman v. Meridian Township, 439 Mich 623, 487 NW2d 155 (1992),
rehearing denied 440 Mich 1204. The case turned on the fact that
the outside land was owned by the developer.
The Subdivision Control Act, MCL 560.182 (4)(a), requires "suitable
access" if the plat or other lands are isolated. The court found
that "suitable access" means more than "any" or "some" access.
Further, the plat violated the road commission requirement for plat
development regarding minimum sight distance. The court contrasted
the Arrowhead case, which addressed off-site improvements in public
right-of-way.
In Troy Campus v. City of Troy, the court stated that problems
along the roadway were created by city land use policies. Thus
they are public problems to by addressed by the public...not
by the last developer.
Site Plan Review
In Charter Township of Harrison v. Calisi, 121 Mich App 777, 329
NW2d 488 (1982), the court applied a rationale similar to that in
Arrowhead to site plan review authority. In Calisi a commercial use
applied for site plan approval for an expansion. The township
required a deceleration lane so vehicles waiting would not disrupt
traffic flow. The court analyzed the township zoning and planning
statutes in a manner similar to the Arrowhead case. The court found
no explicit grant to townships to condition building permits on
off-site improvements and found that no authority should be
Evaluating Traffic Impact Studies: Legal Issues 30
Summary of Michigan Cases and Constitutional Issues:
(1) The Subdivision Control Act does not authorize off-site
improvements, with limited exceptions.
(2) The zoning enabling acts do not authorize off-site
improvements through site plan review.
(3) The Mobile Home Commission Act and its rules do not
authorize off-site improvements to public roads.
(4) The constitutionality of off-site improvements has bee
addressed and upheld under the driveway permit approval
process.
implied in the township acts. The court said that since the
township had no authority to impose the requirement, its theories
for forcing the requirements must fail. The theories would only
apply if authority was granted by.the legislature. Again, ft
appears that specific statutory authority may have resulted in a
different holding.
Jack Loek's Theaters, Inc. v. City of Kentwood 189 Mich App 603,
474 NW2d 140 (1991) is another case involving a requested roadway
improvement as part of a site plan review. The city rejected d site
plan for a shopping center because the plan made no provision for a
public roadway to traverse the property, as shown in the city's
master plan. The court did not address the exaction issue since the
city admitted that the denial was a taking. (The court dealt with
issues of attorney fees and valuation only.)
In addition to the Subdivision Control Act, Michigan courts have
addressed improvements to public roads by developers under the
Mobile Home Commission Act. In Engineered Housing Con Inc. v Wayne
County, 180 Mich App 465, 447 NW2d 777 (1989), the court declined
to uphold a road commission requirement for improvement to a public
road for mobile home park ingress and egress. The Engineered
Housing court referenced the Arrowhead case for the proposition
that absent statutory authority, the county cannot require
improvements outside the development site.
The court found that the definitions of ingress and egress road
adopted by the mobile home commission did not include public roads.
The court cited a number of cases for the proposition that:
"The construction given to a statute by those charged with
duty of executing it is always entitled to great deference and
will not be overturned unless clearly wrong or another
construction is plainly required."
Driveway Permit Process
In Loyer Educational Trust v. Wayne County Road Commission, 168
Mich App 587, 425 NW2d 189 (1988), leave denied 431 Mich 911
(1988), a requirement for off-site improvements was upheld by the
court. The road commission denied a driveway permit to a commercial
development unless the developer made certain modifications to the
road right-of-way, including a passing lane opposite the
development and a widening of the pavement in front of the
development as a deceleration lane to prevent traffic congestion.
The road commission based its requirements on the Michigan
Driveways, Banners, Events and Parades Act, MCL 247.321, et seq.
The court found that the statute provided that no driveway is
lawful except a permit for driveways shall be granted in conformity
with rules promulgated by the highway authority consistent with
public safety and other requirements in the public interest. The
Act allows the Michigan Department of Transportation and boards of
county road commissions to adopt rules under the Act. The Wayne
County Road Commission had adopted rules which
Evaluating Traffic Impact Studies: Legal Issues 31
required a passing lane on the opposite side of the highway from a
proposed commercial driveway when the traffic volume reached
certain limits. The court found the rules were within the authority
conferred by the Act and that the improvements required were
consistent with the rules. The court distinguished the Arrowhead
and Calisi decisions, citing that those cases involved different
statutes and facts. The court summarily found that the denial of
the driveway permit did not constitute the taking of private
property without just compensation under the federal and state
constitutions. It provided no analysis or rationale for its
holding.
Summary of Michigan Cases and Constitutional Issues
Attorneys and planners tend to generalize the findings of a
particular case to broad application. The cases cited above must be
read within the particular context of the facts and statutes which
each presented to the courts. The consultant attorneys consider
only the following generalizations appropriate:
(1) The Subdivision Control Act does not authorize off-site
improvements, unless required on land owned by the developer
or land included by the developer on his plans, as more than a
point of reference.
(2) The zoning enabling acts do not authorize off-site
improvements through site plan review.
(3) The Mobile Home Commission Act and its rules do not authorize
off -site improvements to public roads.
(4) The constitutionality of off-site improvements had been
addressed and upheld under the Driveways, Banners, Events and
Parades Act and has not been addressed in the other cases.
(5) The Driveways, Banners, Events and Parades Act does provide
authority for off-site improvements.
A reasonable reading of Troy Campus suggests that constitutionality
would be upheld if the developer was required to contribute a
proportionate share only. The balance of the cases suggest or
actually state that off-site improvements would be constitutional
if the legislature saw fit to specifically grant authority for such
improvements. Specific authority, coupled with Loyer, may overcome
the Troy Campus limitations, since both Loyer and Troy Campus are
Court of Appeals decisions, but the Supreme Court denied leave to
appeal in Loyer. On the other hand, the constitutional requirements
of federal and Michigan takings cases in general would dictate that
the exaction from the developer must be substantially related to
the particular impact of the development, and requiring correction
of a pre-existing traffic problem would be problematic under the
takings clauses and other constitutional provisions. It the
municipality obtains a greater benefit by imposing conditions than
it would have obtained by denying approval outright, the condition
is not likely to be upheld. One means of establishing
reasonableness is for the
Evaluating Traffic Impact Studies: Legal Issues 32
One technique used by a number of communities to address
traffic issues is through Special Land Use provisions in their
zoning ordinances. The zoning acts state that conditions may
be placed on approval of a special land use to insure public
services can accommodate increased loads caused by the land
use.
municipality to adopt industry accepted standards (e.g., levels of
service) and impose only those conditions necessary to maintain
those standards.
Possible Authority for Requiring Traffic Impact Studies under
Existing Michigan Enabling Legislation
Michigan municipalities do have an effective tool to consider
traffic impact issues through "special land uses." The zoning
enabling acts allow a community to provide for special land uses in
its zoning ordinance. Such uses will only be approved after
discretionary review by the municipality to determine whether the
use complies with requirements, standards and procedures contained
in its zoning ordinance, including requirements for it supporting
materials," which could reasonably include traffic impact studies.
Also, under MCL 125.286d, MSA 5.3963 (16d), "reasonable conditions"
attendant to a special use may include '.conditions necessary to
insure that public services and facilities . . . will be capable of
accommodating increased services and facility loads caused by the
land use or activity." This would reasonably include traffic impact
analyses.
There are no Michigan appellate cases holding that municipalities
lack authority to impose requirements for off-site improvements as
a condition of special land use approval. Any conditions imposed on
special land use approval must be reasonable, however, and must
meet each of the following statutory requirements:
(a) Be designed to protect natural resources, the health,
safety, and welfare and the social and economic well being of
those who will use the land use or activity under
consideration, residents and landowners;
(b) Be related to the valid exercise of the police power, and
purposes which are affected by the proposed use or activity;
(c) Be necessary to meet the intent and purpose of the zoning
ordinance, be related to the standards established in the
ordinance for the land use or activity under consideration,
and be necessary to insure compliance with those standards,"
Municipalities may have difficulty meeting these requirements for
off-site traffic improvements designed to correct existing traffic
problems at the location of the proposed development at the time
the application for special use approval is submitted.
Therefore, under current legislation, Michigan municipalities may
use the special use process for particular uses expected to
generate high volumes of traffic. The zoning ordinance could either
incorporate the model ordinance herein, or make reference to the
model ordinance if adopted as a "stand alone" ordinance. Amendments
to the zoning enabling acts, Subdivision Control Act, Mobile Home
Commission Act, and the Condominium Act to specifically permit off-
site improvements as a condition to development approval would be
necessary to increase and clarify such authority.
Evaluating Traffic Impact Studies: Legal Issues 33
5. Other Techniques to manage Traffic
- Master Plans
- Thoroughfare Plans
- Corridor Plans
- Access Management
- Right of Way Preservation
- Demand Management
- Agency Coordination
Traffic impact studies are only one of many tools that communities
and road agencies should be using to address transportation issues.
Some of the more important tools are summarized below.
Community Master Plans, Thoroughfare Planning and Corridor Plans
Transportation is directly related to decisions about land use.
Land use decisions deal as much with mobility among various
districts of the community as with how the land is used. By
controlling the intensity of land use, the number of trips
generated by the various districts of the community can also be
controlled. The best tool available for this purpose is an
integrated land use/transportation planning process that measures
every decision against a clear, unified vision of the future. The
community's master plan is this vision. Too often, however, the
traffic and transportation consequences of this vision are over-
looked or underestimated.
A well developed Master Plan must consider plans for land use in
the context of transportation planning. In land use planning,
decisions are made about where to locate residential developments,
commercial areas, open spaces, etc. It should also consider the
future transportation advantages of designating certain areas for
higher density. It a community's density is channeled to areas
where traffic can be accommodated by existing transportation
systems or feasible alternatives, lower densities can be preserved
elsewhere in the community.
Evaluating Traffic Impact Studies: Legal Issues 34
Click HERE for graphic.
The circulation portion of the master plan should be used to
analyze the current transportation situation and predict future
demands on R based upon land use designations. Typically, the
circulation plan should address elements such as the following:
- A general facts section: Who has jurisdiction over the roads?
How many miles of roads and in what classifications? What are
the primary sources of road dollars?
- Existing street system analysis and street classification
according to a street hierarchy, taking into account the
functional highway classification system of the Federal
Highway Administration.
- Problem areas such as dangerous curves, accident locations,
and congested intersections or corridors.
- Unique local features impacting transportation: roadway
pavement type, poor sight distance, geographic features which
limit accessibility (rivers), environmental constraints
(wetlands, floodplains, topography), etc.
- Traffic safety concerns.
- Traffic signalization.
- Roadway corridors with deficient rights-of-way.
- Possible alignments for new streets.
- A hierarchy for proposed streets.
- Non-auto transportation modes: transit, light rail, air,
pedestrians, bicycles.
- Urban service boundaries in conjunction with planning for
future transportation and utility extensions.
- Future demands on the transportation system.
- Corridors with insufficient right-of-way to accommodate
expected improvements needed in the future.
- Critical corridors.
- Alternative improvement plans and techniques to handle future
traffic volumes.
- A transportation improvement program for the planning period.
Master planning should identify the amount and type of traffic the
future land use plan will generate and the effects of this added
traffic on the transportation system. The plan can also be used to
establish background traffic levels for critical corridors which
Evaluating Traffic Impact Studies: Legal Issues 35
would then become the basis for developing traffic impact studies.
In this way, the master plan becomes a pro-active tool used to
avoid the congestion and safety hazards that may result from
looking at individual developments rather than the community
development as a whole.
Metropolitan Area and Substate Long Range Transportation Plans
Each urbanized area with a population over 50,000 has a designated
Metropolitan Planning Organization (MPO). The MPO prepares a 20
year Long Range Transportation Plan, typically using a computer
modeling process. In addition, each MPO prepares a three year
Transportation Improvement Program (TIP) which lists project
priorities for funding.
The Michigan Department of Transportation is required by the
federal lntermodal Surface Transportation Efficiency Act (ISTEA) to
prepare a Statewide Long Range Transportation Plan.
Community leaders should ensure that important transportation
projects and issues are considered and addressed in these Long
Range Transportation Plans.
Roadway widening is not the only way to address congestion. A
number of other traffic management techniques are being used
in Michigan and other states.
Corridor Right-Of-Way Preservation and Corridor Management
Many roadways in Michigan were originally designed for much lower
traffic volumes than they are now expected to accommodate.
Improvements to these roadways are often limited due to lack of
right-of-way or development which lines the roadway.
The lack of adequate right-of-way escalates costs and significantly
delays improvement projects. One way to minimize these problems is
through a cooperative effort to preserve right-of-way. In many
Michigan communities, developers provide additional right-of-way in
recognition of the benefits they could receive in the future.
Communities and road agencies, however, need to be careful to avoid
unnecessary "taking" of private property.
The Michigan Department of Transportation has developed one process
to help preserve right-of-way through public-private cooperation.
The process provides the developer with incentives to preserve or
dedicate needed additional right-of-way. For example, a community
might allow a developer to transfer the development that could
occur in the future right-of-way to another location on the site.
Successful right-of-way preservation in this manner requires a
specific time frame for corridor improvement.
This procedure is currently being used along M-59 in Livingston
County. A multi-jurisdictional corridor advisory committee reviews
development proposals along the corridor and provides guidance and
comments regarding right-of-way preservation and access management.
Evaluating Traffic Impact Studies: Legal Issues 36
Transportation Demand Management
Transportation demand management includes a coordinated program to
improve the movement of goods and people through a more efficient
use of the existing transportation system. The goal is to reduce
the number of vehicle miles traveled, i.e., transportation demand.
- a program to reduce single occupant vehicles (SOVS) through
car pools, van pools, transit, cycling, etc.
- working with large employers to improve telecommunications as
a substitute for vehicle trips (telecommuting)
- developing a coordinated program of staggered work shifts and
flextime to "flatten" the peak hour traffic curve
- providing incentives to encourage use of park and ride
facilities such as preferred parking or cash incentives
- encourage sidewalk and bikepath connections between
developments
- support designs which encourage transit use and site design
sensitive to the needs of transit vehicles
Michigan's first significant transportation demand management
program has been started in Oakland County. This program is being
applied to areas with "critical traffic congestion."
One mitigation technique to reduce peak hour traffic impacts being
used in a number of California, Oregon and New Jersey communities
is a "Traffic Management Ordinance" or "Trip Reduction Ordinance."
These ordinances typically apply to small/medium sized
developments. The ordinances include incentives for ride sharing
(such as preferential parking for car and vanpoolers) and
requirements for specified percentages of the work force to have
shifts at off-peak hours. Corporations are required to provide
traffic management operation plans. Fines are imposed for
developments which will not or cannot comply with the ordinance.
Oregon has requirements that communities must use demand management
to reduce traffic volumes over the next 20 years.
No community in Michigan has taken the step of imposing a trip
reduction ordinance. Fortunately, a number of Michigan corporations
have undertaken trip reduction programs on their own, such as
Steelcase in the Grand Rapids area. There are a number of public
agencies that can assist in car and van pooling efforts.
Access Management
Access management involves comprehensive controls over all aspects
of roadway access to help preserve the traffic carrying
Evaluating Traffic Impact Studies: Legal Issues 37
function for which the roadway was designed. Access management
recognizes that while the land owner has a right to reasonable
access, the primary function of arterial roadways is to move
traffic. Two key reasons for access management are to improve
safety and to preserve capacity. Case studies have shown that
roadways utilizing access management techniques have
experienced significantly lower crash rates and significantly
improved capacity in comparison with similar streets not
utilizing access management.
Access management typically involves local ordinances and road
agency standards to limit the number of traffic conflict
points and to separate conflict points. The types of access
management standards are usually based on the operational and
physical characteristics of the roadway. Typical access
management techniques include:
- the number of site access points
- driveway spacing from intersections
- driveway spacing and offsets from other driveways
- use of alternative access such as frontage roads, rear service
drives and shared driveways
- spacing of expressway interchanges
- spacing of traffic signals to ensure good progression
- use of medians to limit left turns
- location, spacing and design of median openings
- standards for bypass lanes and deceleration lanes/tapers
- require access connection to side street rather than arterial
- driveway geometry and grades
Statewide access management standards are used in several
states. The Michigan Department of Transportation expects to
have a State Access Code by 1995. Several Michigan road
commissions and communities have developed various types of
access management regulations or guidelines (listed in
Bibliography). A model zoning ordinance for community access
management is also available through the Tri-County Regional
Planning Commission at the address and phone number shown
inside the front cover.
Click HERE for graphic.
Zoning Techniques
In addition to introducing uniform traffic impact study
requirements through the zoning ordinance, there are a number
of other zoning techniques which a community should consider:
- Encouraging mixed use developments through Planned Unit
Development or cluster zoning options. A study published by
the American Society of Civil Engineers demonstrated that
mixed use developments resulted in 25% less vehicle delay and
20% fewer trips generated than associated with typical
segregated development patterns.
Classify high traffic generating uses as Special Land Uses.
Evaluating Traffic Impact Studies: Legal Issues 38
- Consider using Corridor Overlay Zoning Districts along
critical corridors. The overlay district could include special
requirements for access management, setbacks, right-of-way
preservation, etc.
- Access management standards as part of the site plan review
process or as a separate set of standards.
Transportation Utility Fees and Impact Fees
Several states have developed legislation which authorizes the
use of "impact fees." New Developments are charges fa fee that
in turn is used to help fund roadway improvements.
Several communities outside Michigan have established
transportation "utility fees" for road use similar to fees charged
for tapping into water and sanitary sewer lines. This is generally
considered to be a user fee, not a tax. A monthly or annual fee is
charged based on the type of use and the functional classification
of the road accessing the use. The money generated is used to
address existing traffic problems and ongoing maintenance of the
roadway system.
Though not used in Michigan, some other states have enabling
legislation which authorize use of Impact Fees. Communities or road
agencies charge new developments a fee, usually based on a trip
generation factor or per unit cost. Monies generated by the impact
fee are used to fund roadway improvements.
Coordination with Other Agencies and Adjacent Communities
Local land use decisions affect not only local traffic conditions
but regional and state transportation systems and conditions within
adjacent communities as well. Significant development proposals and
their potential traffic impacts must, therefore, be coordinated and
reviewed by all affected jurisdictions.
Monitoring Traffic Conditions/Data Management
Both communities and road agencies need to collect and maintain
traffic data. Data assists in developing traffic impact studies and
meeting the requirements of the lntermodal Surface Transportation
Efficiency Act (ISTEA). Among the activities which should be
considered are:
- traffic count programs;
- recording of traffic crashes;
- pavement condition inventory;
- monitoring volume/capacity ratios.
Evaluating Traffic Impact Studies: Legal Issues 39
Appendices
I. Model Ordinance
II. Checklist and Forms
III. References
Evaluating Traffic Impact Studies: Appendices A1
1. MODEL TRAFFIC IMPACT STUDY ORDINANCE
The model ordinance language on the following pages is based on the
thresholds and other standards suggested in this handbook. The
model ordinance language would typically be adopted as part of the
zoning ordinance either as a General Provision or as a separate
chapter. If this approach is used, the local Subdivision Control
and Condominium Ordinances, if separate, should reference these
requirements. The requirements for an impact study, such as for a
PUD, could also reference these standards for the traffic section.
Individual communities may wish to tailor the model to meet
particular needs.
Among the sections a community may wish to modify are:
- The ordinance could be shortened if referencing this handbook
for items such as "Traffic Impact Study Analyses."
- High traffic generating uses could be identified as Special
Land Uses, within the zoning district, with a traffic impact
study listed as one of the required submittal items for those
uses.
- A traffic impact study may not be needed for a rezoning
request which is consistent with the Master Plan.
- Thresholds for when a study is required (refer to Table 2).
- Could specify that traffic studies are required along certain
corridors based on the Master Plan.
- The extent of information required, particularly analysis of
crash data.
- A review of Transportation Demand Management (TDM) could
be required for employment centers in congested areas.
- Charts from the handbook could be included with the
ordinance or attached to an application form, particularly
Table 3 and the procedure flowchart. This would help clarify
the different types of traffic studies required by the
ordinance.
- Communities with traffic engineering staff may desire local
trip
generation data to supplement or replace national sources.
- The review process may vary, such as other agencies which
receive a copy of the study.
The Model Traffic Impact Study Ordinance is basically set up for
the most common type of study - the Traffic Impact Statement. The
ordinance acknowledges some of the study differences, such as less
detail for a rezoning traffic study.
The ordinance could be refined to further distinguish requirements
for different types of impact studies. Other options include
referencing the handbook and/or Table 3 as part of the zoning
ordinance.
Evaluating Traffic Impact Studies: Appendix I - Model Ordinance A2
The model ordinance can also be adopted into specific sections of
the zoning ordinance. For example, the traffic thresholds for
rezonings could be placed in the "Ordinance Amendment" section, and
other thresholds could be placed in the site plan review submittal
requirements section. Both of these sections could reference a
General Provision section which describes the requirements for a
traffic impact study.
Certain high traffic generating uses could be treated as Special or
Conditional Land Uses, which require a traffic impact study as part
of the submittal package.
Evaluating Traffic Impact Studies: Appendix I - References A3
Model Traffic Impact Study Ordinance
Sec. 101 Intent
(Community name) recognizes the direct correlation between land use
decisions and traffic operations. The intent (chapter, article or
section) is to permit accurate evaluation of expected impacts of
proposed projects to assist in decision-making. This ordinance is
further intended to help achieve the following objectives:
- Provide a standard set of analytic tools and format for
preparing traffic impact studies.
- Allow the community to assess the effects that a proposed
project may have on the community by outlining information
needed and evaluation procedures to be used.
- Help ensure safe and reasonable traffic operating conditions
on streets and intersections after development of the proposed
use.
- Reduce the negative traffic impacts created by individual
developments, and which may negatively impact such
developments, by helping to ensure the transportation system
can accommodate the expected traffic safely and efficiently.
- or rezonings, the traffic impact study is intended to evaluate
if the rezoning is timely and, if inconsistent with the master
plan, if the rezoning would be a logical alternative to the
master plan.
- Realize a comprehensive approach to the overall impacts of
various developments along a corridor or within part of a
community rather than a piecemeal approach.
- Provide direction to community decision makers, road agencies
and developers of expected impacts of a project.
- Alert the community, transportation agencies, and developers
of improvements or modifications needed to the roadway, access
or site design.
- Protect the substantial public investment in the existing
street system.
Sec. 102 Definitions
The following terms used in this ordinance shall be defined as
follows:
Development: A site plan, subdivision tentative preliminary plat,
condominium project, mobile home park, redevelopment, reuse or
expansion of a use or building.
Average Day: A Tuesday, Wednesday, or Thursday for most uses.
The average day may be a Saturday for uses that have higher peak-
hour traffic volumes on a Saturday rather than mid-week.
Gap (critical gap): The median time headway (in seconds) between
vehicles in a major traffic stream which will permit side-street
vehicles at STOP or YIELD controlled approach to cross through or
merge with the major traffic stream under prevailing traffic and
roadway conditions.
Level of service: A qualitative measure describing operational
conditions within a traffic stream; generally
described in terms of such factors as speed and travel time, delay,
freedom to maneuver, traffic interruptions, comfort and
convenience, and safety.
Master Plan: The plan adopted by the (community name) Planning
Commission which illustrates the intended future land use pattern
and may also describe roadway functional classifications and
intended improvements to the transportation system (i.e.,
Comprehensive Plan, Future Land Use Plan, Thoroughfare Plan, etc.)
Evaluating Traffic Impact Studies: Appendix I - Model Ordinance A4
Peak Hour: A one hour period representing the highest hourly
volume of traffic flow on the adjacent street system during the
morning (a.m. peak hour), during the afternoon or evening (p.m.
peak hour); or representing the hour of highest volume of traffic
entering or exiting a site (peak hour of generator).
Study Area: The geographic area containing those critical
arterial intersections (and connecting roadway segments) which are
expected to be affected by the site-traffic generated by a
development.
Traffic Impact Study: The analysis of the potential traffic
impacts generated by a proposed project. This type of study and
level of analysis will vary dependent upon the type and size of the
project - Traffic Impact Assessment, Rezoning Traffic Impact Study,
Traffic Impact Statement, and Regional Traffic Impact Study.
Trip (i.e., directional trip): A single or one-direction
vehicle movement with either the origin or the destination (exiting
or entering) inside a study site.
Sec. 103 Applicability
A traffic impact study shall be required and shall be submitted by
a petitioner for a rezoning, site plan or subdivision plan under
any of the following situations. The type of study required shall
be dependent upon the type and scale of the proposed use and
existing traffic conditions.
a. A "Rezoning Traffic Impact Study" for the following Rezonings
and Master Plan amendment requests:
1. A proposed rezoning consistent with the community's long
range land use plan, but when the timing of the change
may not be appropriate due to traffic issues. This
threshold applies when a rezoning would permit uses that
could generate 100 or more directional trips during the
peak hour, or at least 1000 more trips per day, than the
majority of the uses that could be developed under
current zoning.
2. A proposed rezoning which is inconsistent with the
community master plan when permitted uses could generate
at least one hundred (1 00) directional trips during the
peak hour of the traffic generator or the peak hour on
the adjacent streets or over seven hundred fifty (750)
trips in an average day.
3. A site along any corridor identified as a
critical/congested/safety management corridor in the
Master Plan or Long Range Transportation Plan.
4. Proposed amendments to the Master Plan which would
recommend uses which would generate higher traffic
volumes.
b. Development Proposals: site plans, plats, mobile home parks
and condominium projects
1. A Traffic Impact Statement shall be required for any
proposed development which would be expected to generate
over one hundred (1 00) directional trips during the peak
hour of the traffic generator or the peak hour on the
adjacent streets, or over seven hundred fifty (750) trips
in an average day.
2. A Traffic Impact Assessment shall be required for
projects which could generate 50-99 directional trips
during a peak hour.
3. A Traffic Impact Statement shall be required for any
proposed development along a corridor identified in the
Master Plan or Long Range Transportation Plan as a
Critical, Congested, or Safety Management Corridor
(segments which currently experience, or are projected to
experience, significant congestion or relatively high
crash rates) which would be expected to generate over
fifty (50) directional trips during the peak hour of the
traffic generator or the adjacent streets, or over five
hundred (500) trips in an average day.
Evaluating Traffic Impact Studies: Appendix I - Model Ordinance A5
4. A Traffic Impact Statement or Assessment, based on the
thresholds in 1 and 2 above, shall be required for new
phases or changes to a development where a traffic study
is more than two (2) years old and roadway conditions
have changed significantly (volumes increasing more than
2 percent annually).
5. A Traffic Impact Assessment shall be required for a
change or expansion at an existing site where the
increased land use intensity is expected to increase
traffic by at least fifty (50) directional trips in a
peak hour or result in at least 750 vehicle trips per day
for the entire project. A Traffic Impact Statement shall
be required if the traffic is expected to increase by
over I 00 directional trips in the peak-hour.
6. Special (conditional) land uses, planned unit
developments, and other uses which are specifically
required to provide a traffic impact study in the zoning
ordinance. The type of study shall be based on the
thresholds in Items 1 and 2.
7. A change in a Planned Unit Development (PUD) to a more
intense use (Note: on a case-by-case basis or using
thresholds similar to those above).
8. Where required by the road agency to evaluate access
issues.
Sec. 104 Traffic Impact Study Contents:
a. Description of the site, surroundings, and study
area: Illustrations and a narrative should describe the
characteristics of the site and adjacent roadway system
(functional classification, lanes, speed limits, etc.). This
description should include surrounding land uses, expected
development in the vicinity which could influence future
traffic conditions, special site features and a description of
any committed roadway improvements. The study should define
and justify the study area selected for analysis.
b. Description of the requested zoning or use
1. Traffic study for a rezoning or Master Plan amendment
request: a description of the potential uses which would
be allowed, compared to those allowed under current
zoning. If the use is not consistent with the
community's master plan, an explanation of the difference
should be provided.
2. Traffic study for a site plan review, mobile home park,
condominium project or subdivision tentative preliminary
plat, or specified Special Land Uses: a description of
factors such as the number and types of dwellings units,
the gross and usable floor area, the number of employees
and shift change factors. Intended phasing or future
expansion should also be noted.
c. Description of existing traffic conditions
1. Traffic counts: Existing conditions including
existing peak-hour traffic volumes (and daily volumes if
applicable) on street(s) adjacent to the site. Existing
counts and levels of service for intersections in the
vicinity which are expected to be impacted, as identified
by the community at a pre-application conference or
discussion, should be provided for projects requiring a
Traffic Impact Statement or Regional Traffic Analysis.
Traffic count data shall not be over two (2) years old,
except the community or road agency may permit 24 hour
counts up to three (3) years old to be increased by a
factor supported by documentation or a finding that
traffic has increased at a rate less than two percent
(2%) annually in the past three to five years.
Traffic counts shall be taken on a Tuesday, Wednesday or
Thursday of non-holiday weeks. Additional counts (i.e. on a
Saturday for a proposed commercial development) may also be
required in some cases. The individual or firm performing the
impact study shall obtain the traffic counts during average or
higher than average volume conditions (i.e. regarding weather
or seasonal variations and in consideration of any
construction or special events) for ,he area under study.
Evaluating Traffic Impact Studies: Appendix I - Model Ordinance A6
2. Roadway characteristics shall be described and
illustrated, as appropriate. Features to be addressed
include lane configurations, geometries, signal timing,
traffic control devices, posted speed limits, average
running speeds and any sight distance limitations.
Existing levels of service shall be calculated for
intersections included within the study area.
3. Existing driveways and potential turning movement
conflicts in the vicinity of the site shall be
illustrated and described.
4. The existing right-of-way shall be identified along with
any planned or desired expansion of the right-of-way
requested by the applicable road agency.
5. Traffic crash data and analysis covering the most recent
three (3) years for the study area or proximity to site
access points may be required by the community,
particularly for sites along roadways identified as
Critical or Congested Corridors. (Note: crash analyses
are not generally appropriate for a Rezoning Traffic
Study or a Traffic Impact Assessment)
d. Background Traffic Growth
For any project requiring a Traffic Impact Statement with a
completion date beyond one (1) year at the time of the traffic
study, the analysis shall also include a scenario analyzing
forecast traffic at date of completion along the adjacent street
network using a forecast based on a network traffic assignment
model (it available), historic annual percentage increases and/or
future development in the area which has been approved. For
project requiring a Regional Traffic Analysis available long range
traffic projections shall be used.
e. Trip Generation
1. Forecasted trip generation of the proposed use for the
a.m.(if applicable) and p.m. peak hour and average day.
The forecasts shall be based on the data and procedures
outlined in the most recent edition of Trip Generation
published by the Institute of Transportation Engineers
(ITE). The applicant may use other commonly accepted
sources of data or supplement the standard data with data
from at least three (3) similar projects in Michigan.
2. For rezoning requests where a traffic study is required,
the study should contrast the traffic impacts of typical
uses permitted in the requested zoning district with uses
permitted in the current zoning district. The
determination of typical uses shall be made by the
(Planning Commission, Planning Director, etc.). For
Traffic Impact Assessments, Statements, or Regional
Traffic Analyses, the rates for the specific use(s)
proposed shall be used.
3. Any trip reduction for pass-by trips, transit,
ridesharing, other modes, internal capture rates, etc.
shall be based both on ITE findings and documented survey
results acceptable to the agency reviewers. The
community may elect to reduce the trip reduction rates
used.
4. For projects intended to be developed in phases, the trip
generation by phase shall be described.
f. Trip Distribution
The projected traffic generated shall be distributed (inbound v.
outbound, left turn v. right turn) onto the existing street network
to project turning movements at site access points, and nearby
intersections where required. Projected turning movements shall be
illustrated in the report. A description of the application of
standard engineering procedures for determining the distribution
should also be attached (trip distribution model, market studies,
counts at existing driveways, etc.). For projects requiring a
Regional Traffic Analysis, use of a network traffic assignment
model projection (if available) may be required to help evaluate
impacts.
Evaluating Traffic Impact Studies: Appendix I - Model Ordinance A7
g. Impact Analysis
1. Level of service or "capacity" analysis at the proposed
access points using the procedures outlined in the most
recent edition of the Highway Capacity Manual published
by the Transportation Research Board. For projects
requiring a Traffic Impact Statement or Regional Traffic
Analysis, before and after capacity analyses shall also
be performed for all street intersections where the
expected traffic generated at the site will comprise at
least five percent (5%) of the existing int
