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CITY OF RENTON Ι PERMIT SERVICES
POLICY GUIDELINES FOR TRAFFIC IMPACT
ANALYSIS FOR NEW DEVELOPMENT
A traffic impact analysis is required when estimated vehicular traffic generated from a proposed development exceeds
20 vehicles per hour in either the AM (6:00 ‐ 9:00) or PM (3:00–6:00) peak periods. A peak hour volume of 20 vehicles
per hour would relate to daily volume of approximately 200 vehicles per day. Generally this includes residential plats
of 20 lots or more and commercial sites that generate 20 vehicles per hour. The developer shall select a registered
professional engineer with adequate experience in transportation planning and traffic engineering. Upon request, the
Public Works Department will offer potential candidates. The analysis shall incorporate the following elements in the
suggested format:
1.Introduction: The introduction should, in a narrative fashion with graphics where appropriate to enhance the text,
describe the proposed development (including proposed time frame), establish study area boundaries (study area
should include all roadways and intersections that would experience a 5% increase in peak hour traffic volumes as
a result of the proposed development), describe existing and proposed land uses within the study area, and
describe the existing transportation system to include transit routes, roadway and intersection conditions and
configuration as well as currently proposed improvements. Roadways and intersections to be analyzed will be
determined through coordination with the Public Works Department and Community Development staff.
2.Site Generated Traffic Volumes: The analysis should present a tabular summary of traffic generated from the
proposed development listing each type of proposed land use, the units involved, trip generation rates used (to
include total daily traffic, AM peak hour and PM peak hour) and resultant trip generation for the time periods
listed. The trip generation information provided in the traffic impact study must be based on the current edition of
the ITE Trip Generation book. Site Generated Traffic Distribution: The distribution of site‐generated traffic should
be presented by direction as a percentage of the total site generated traffic in a graphic format. The basis for the
distribution should be appropriately defined.
3.Site Generated Traffic Assignment: A graphic presentation should be provided illustrating the allocation of site‐
generated traffic to the existing street network. The presentation should include Average Daily Traffic (ADT) and
AM‐PM peak hour directional volumes as well as turning movements at all intersections, driveways, and roadways
within the study area. Existing and Projected Horizon Year Traffic Volumes With and Without the Proposed
Development: The report should include graphics, which illustrate existing traffic volumes as well as forecasted
volumes for the horizon year of the proposed development. Forecasted volumes should include a projected
growth rate and volumes anticipated by pending and approved developments adjacent to the proposed
development. If the development is multi‐phased, forecasted volumes should be projected for the horizon year of
each phase. The site‐generated traffic should then be added to the horizon year background traffic to provide a
composite of horizon year traffic conditions.
4.Condition Analysis: Based upon the horizon year traffic forecasts with the proposed development, a level of
service (LOS) analysis should be conducted at all intersections (including driveways serving the site). Based upon
this analysis, a determination should be made as to the ability of the existing and proposed facilities to handle the
proposed development. The level of service (LOS) analysis technique may include any of the commonly accepted
methods. An analysis should be made of the proposed project in light of safety. Accident histories in close
proximity to the site should be evaluated to determine the impact of proposed driveways and turning movements
on existing problems.
5.Mitigating Measures: Based upon the results of the previous analysis, if it is determined that specific roadway
improvements are necessary, the analysis should determine what improvements are needed. If the developer can
reduce vehicular traffic by means of promoting transit and ridesharing usage, these methods are acceptable. Any
proposed traffic signals should be documented with an appropriate warrant analysis of conditions in the horizon
year with the development. Traffic signals should not be contemplated unless they meet warrants as prescribed in
the Federal Highways “Manual on Uniform Traffic Control Devices”. Proposed traffic signals shall provide
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TRANSPORTATION IMPACT ANALYSIS GUIDELINES
coordination programs to compliment the system. Any modifications necessary to insure safe and efficient
circulation around the proposed site should be noted.
6.Conclusions: This section should serve as an executive summary for the report. It should specifically define the
problems related directly to the proposed developments and the improvements necessary to accommodate the
development in a safe and efficient manner. A draft report shall be presented to the Development Engineering
Division so that a review might be made of study dates, sources, methods, and findings. City Staff will then provide
in writing all comments to the developer. The developer will then make all necessary changes prior to submitting
the final report.