TrafficFOR DEMONSTRATION PURPOSES, ONLY
CITY OF OLYMPIA
Traffic Impact Analysis (TIA)
Guidelines for New Developments
A. INTRODUCTION
A traffic impact analysis (TIA) is a specialized study of the impacts a certain type and size of development
will have on the surrounding transportation system. The traffic impact analysis is an integral part of the
development impact review process. It is specifically concerned with the generation, distribution, and
assignment of traffic to and from the "new development." The purpose of a TIA is to determine what
impact development traffic will have on the existing and proposed street network and what impact the
existing and projected traffic on the street system will have on the "new development."
These guidelines have been prepared to establish the requirements for a Traffic Impact Analysis. The
Environmental Review Officer (ERO) will be the person responsible under SEPA as well as city
ordinances for determining the need for a Traffic Impact Analysis. The transportation division will have a
significant role during the TIA process also.
B. WHEN REQUIRED
To adequately assess a "new development" traffic impact on the transportation system and level of traffic
service, the Environmental Review Officer (ERO) may require a traffic impact analysis (TIA). The
requirement for a TIA will be based on the size of the development proposed, existing street and
intersection conditions, traffic volumes, accident history, community concerns, and other pertinent factors
relating to traffic impacts attributable to "new developments."
The following is a fist of specific conditions that may dictate the requirement for preparing a TIA. The
ERO may require the preparation of a TIA if one or more of the following conditions are satisfied:
The "new development" generates more than 20 vehicles in the peak direction of the peak hour
on the adjacent streets and intersections. This would include the summation of all turning
movements that affect the peak direction of traffic.
2. The "new development" generates more that 25% of site-generated peak hour traffic through a
signalized intersection or the "critical" movement at an unsignalized intersection.
3. The "new development" is within an existing or proposed transportation benefit area. This may
include Latecomer Agreements, Transportation Benefit Districts. (TBD), Local Improvement..
Districts (LID), or local/state transportation improvement areas programmed for development
reimbursements.
4. The "new development" may potentially affect the implementation of the street system outlined in
the Transportation element of the Comprehensive Plan, the Transportation Improvement
Program, or any other documented transportation project.
5. The "new development" proposes a rezone of the subject property.
6. The original TIA is more than two years old or where the proposed land use intensity increased
by more than 10%.
If the ERO has made the determination to require a TIA, the general guidelines to content and structure
shall follow the format outlined in Section D. Scope of Work.
C. QUALIFICATIONS FOR PREPARING TIA DOCUMENTS
Traffic Impact Analyses (TIA) shall be conducted under the direction of a responsible individual or firm
acceptable to the ERO, Transportation Division Manager, or Public Works Director. The TIA shall be
prepared by an engineer licensed to practice in the State of Washington with special training and
experience in traffic engineering and who is a member of the Institute of Transportation Engineers (ITE).
The developer shall provide the ERO the credentials of the individual(s) selected to perform the TIA.
Upon request, the ERO may provide the developer a list of qualified individuals to perform such work.
D. SCOPE OF WORK
The level of detail and scope of work of a TIA may vary with the size, complexity, and location of the "new
development". A TIA shall be a thorough review of the immediate and long-range effects of the "new
development" on the transportation system.
1. "New Development" Prospectus
a. Provide a reduced copy of the "Site Plan" showing the type of development, street
system, right-of-way limits, access points, and other features of significance in the "new
development". The "Site Plan" shall also include pertinent "off-site" information such as
locations of adjacent intersections, land-use descriptions, street right-of-way limits with
respect to the existing roadway and other features of a significance. Exhibit "A"
illustrates an example site plan for reference purposes.
b. Provide a "Vicinity Map" of the project area showing the transportation system to be
impacted by the development. Exhibit "B" illustrates an example vicinity map for
reference purposes.
c. Discuss specific development characteristics such as type of development proposed
(single-family, multi-family, retail, industrial etc.), internal street network, proposed access
locations, parking requirements, zoning, and other pertinent factors attributable to the
"new development."
d. Discuss project completion and occupancy schedule for the "new development." Identify
horizon years for traffic analysis purposes.
2. Existing Conditions
a. Discuss street characteristics including functional classification, number of traveled lanes,
lane width, shoulder treatment, bicycle path corridors and traffic control at study
intersections. A "Figure" may be used to illustrate existing transportation facilities.
b. Identify safety and access problems including discussions on accident history, sight
distance restrictions, traffic control, and pedestrian conflicts.
c. Obtain all available traffic data from the City of Olympia. If data is unavailable, the
individual or firm preparing the TIA shall collect the necessary data to supplement the
discussions and analysis in the TIA.
d. Conduct manual peak hour turning movement counts at study intersections if traffic
volume data is more than 2 years old unless otherwise required by the ERO. A copy of
the reduced data shall be attached to the TIA when submitted to the ERO for review.
e. A "Figure" shall be prepared showing existing average daily traffic (ADT) and peak hour
traffic volumes on the adjacent streets and intersections in the study area. Complete
turning movement volumes shall be illustrated as shown in Exhibit "C". This "Figure"
shall represent the "base-line" traffic volumes for analysis purposes.
3. Development Traffic
This element of the TIA shall be conducted initially to identify the limits of the study area. The study area
shall include all pertinent intersections and streets impacted by development traffic. The limits of the
study area shall be representative of the specific conditions outlined in Section B. of these guidelines.
The threshold requirement of development traffic exceeding 20 vehicles in the peak direction of the peak
hour on the adjacent streets and intersections shall apply. The threshold requirement of the development
generating 25% or more of site traffic through a signalized intersection or the "critical" movements at an
unsignalized intersection shall also apply. Each intersection and street impacted as described shall be
included in the study area for analysis purposes.
The individual or firm preparing the TIA shall submit to the ERO a "Figure" illustrating the proposed "trip
distribution" for the new development. The trip generation shall be included in a table format on the
"Figure" with the peak hour traffic volumes assigned to the study area in accordance with the trip
distribution. Once approved by the ERO, a formal "scoping" of the development proposal shall be
conducted to clearly identify the study area and contents expected in the TIA. Exhibit "D" shows an
example "Figure" for reference purposes.
The methodology and procedures used in preparing the trip generation and trip distribution elements of
the TIA are as follows:
a. Trip Generation
Site-generated traffic of "new developments" shall be estimated using the latest edition of the ITE
TRIP GENERATION MANUAL., Variations of trip rates will require the approval of the ERO and
transportation division. Average trip rates shall be used for all land-use categories where
applicable. Trip rate equations will be allowed for those land-uses without average rates.
Site traffic shall be generated for daily and A.M. and P.M. peak hour periods. Adjustments made
for "passer-by" and "mixed-use" traffic volumes shall follow the methodology outlined in the latest
edition of the ITE TRIP GENERATION MANUAL. A "passer-by" traffic volume discount for
commercial centers shall not exceed 25% unless approved by the ERO.
For multi-use and/or "phased" projects, a trip generation table shall be prepared showing
proposed land-use, trip rates, and vehicle trips for daily and peak hour periods and appropriate
traffic volume discounts if applicable.
b. Trig Distribution
The trip distribution for a new development shall be approved by the ERO and prior to the formal
scoping of the TIA. The methodology shall be clearly defined and discussed in detail in the TIA.
Information on transportation modeling, regional distribution models, transportation analysis
zones, and employment density areas are available from the Thurston County and City of
Olympia Planning Departments. Available information can be used to assist in the preparation of
the trip distribution model. A regional trip distribution map may be required by the ERO for large
scale development projects. Exhibit "E" shows an example "Figure" for reference purposes.
The TIA shall identify other transportation modes that may be applicable, such as transit use,
bicycle and pedestrian facilities. New developments are encouraged to implement Transportation
Demand Management practices such as "Flex Time" for employees and ridesharing programs
including carpools, van pools, shuttle buses etc.
4. Future Traffic
a. Future Traffic Conditions Not Including Site Traffic
Future traffic volumes shall be estimated using information from transportation models or
applying an annual growth rate to the base-line traffic volumes. The future traffic
volumes shall be representative of the horizon year for project development. The ERO
will determine an appropriate growth rate, if that option is utilized.
In addition, proposed "on-line" development projects shall be taken into consideration
when forecasting future traffic volumes. The increase in traffic from proposed "on-line"
projects shall be compared to the increase in traffic by applying an annual growth rate.
If modeling information is unavailable, the greatest traffic increase from either the "on-
line" developments or the application of an annual growth rate shall be used to forecast
the future traffic volumes.
b. Future Traffic Conditions Including Site Traffic
The site-generated traffic shall be assigned to the street network in the study area based
on the approved trip distribution model. The site traffic shall be combined with the
forecasted traffic volumes to show the total traffic conditions estimated at development
completion. A "Figure" will be required showing daily and peak period turning movement
volumes for each traffic study intersection. Exhibit "F" shows an example "Figure" for
reference purposes. In addition, a "Figure shall be prepared showing the base-line
volumes with site-generated traffic added to the street network. This ~~Figure" will
represent site specific traffic impacts to existing conditions.
5. Traffic Operations
The Level of Service (LOS) and capacity analysis shall be conducted for each pertinent intersection in the
study area as determined by the ERO and transportation division. The methodology and procedures for
conducting the capacity analysis shall follow the guidelines specified in the Highway Capacity Manual-
Special Report 209, 1985 Manual. The individual or firm preparing the TIA shall calculate the
intersection LOS for each of the following conditions:
a. Existing peak hour traffic volumes ("Figure" required).
b. Existing peak hour traffic volumes including site-generated traffic ("Figure"
required).
c. Future traffic volumes not including site traffic ("Figure" required).
d. Future traffic volumes including site traffic ("Figure" required).
e. Level of Service results for each traffic volume scenario ("Table" required).
The Level of Service table shall include LOS results for A.M. and P.M. peak periods if applicable. The
table shall show LOS conditions with corresponding vehicle delays for signalized intersections and LOS
conditions for the critical movements at unsignalized intersections. For signalized intersections, the LOS
conditions and average vehicle delay shall be provided for each approach and the intersection as a
whole.
The capacity analyses for existing signalized intersections shall include existing phasing, timing, splits
and cycle lengths in the analysis as observed and measured during the peak hour traffic periods. All
traffic signal system operational data will be made available by the City of Olympia.
If the "new development" is scheduled to be completed in phases, the TIA shall conduct a LOS analysis
for each separate development phase. The incremental increases in site traffic from each phase shall be
included in the LOS analysis for each proceeding year of development completion. A "Figure" will be
required for each horizon year of "phased" development.
If the "new development" impacts a traffic signal coordination system currently in operation, the ERO may
require the TIA to include operational analysis of the system. Timing plans and proposed modifications to
the coordination system may be required.
The capacity analysis shall be conducted using computer software compatible with the transportation
division's software package. The individual or firm preparing the TIA shall use SIGNAL85,
Version 2, for capacity analysis of study intersections. The computer worksheets, along with a
3 1/2" floppy disk of each capacity analysis, shall be submitted concurrently with the TIA document to
the ERO and transportation division. For unsignalized intersections, the "Highway Capacity
Manual" methodology shall be used. A copy of the capacity analyses worksheets shall be submitted
concurrently with the TIA document.
Other computer software packages used for capacity analysis applications will not be accepted.
6. Mitigation
The TIA shall include a proposed mitigation plan. The mitigation may be either the construction of
necessary transportation improvements or contributions to the City for the "New developments" fair
share cost of identified future transportation improvements. Level of Service "E" and "F" shall be
used as the threshold for determining appropriate mitigating measures on roadways and
intersections in the study area. Mitigating measures shall be required to the extent that the
transportation facilities operate at a Level of Service "D" condition or better.
The following guidelines shall be used to determine appropriate mitigating measures of traffic impacts
generated by new developments.
On transportation facilities where the need to construct improvements, by the horizon
year of the "new development", the cost for the mitigation will be entirely born by the
"new development". However, in the event the ERO officer and the transportation
division identifies more than one development under simultaneous review,
accumulative impacts and distribution of mitigation costs may be considered. A
latecomers agreement could be formulated by the "new development" for
reimbursement for mitigation costs.
2. On transportation facilities programmed for new improvements as part of a City project,
the adverse traffic impacts of the "new development" will be considered mitigated by
providing a proportionate share contribution of the costs for the proposed
improvements. The proportionate share costs for the improvements shall be based on
the percentage of "new development" traffic generated through the intersection. The
percentage shall be based on the total projected peak hour traffic volumes for the
horizon year of the transportation facility.
If the transportation facility currently operates less than Level of Service "D," the
"new development" shall be required to make interim facility improvements to
maintain the existing level of service operation on the facility. The cost of the
interim improvements will be deducted from the "new developments" proportionate
share of costs for the programmed facility improvements only if the cost of the
interim improvements is less than the ultimate proportionate share. If the interim
improvements cannot be incorporated into the ultimate improvements programmed
for the transportation facility, there will be no reimbursement for interim costs
incurred.
3. On transportation facilities where the existing Level of Service condition is less than
LOS "D", and where no improvements are programmed to improve capacity and
traffic operations, the "new development" shall mitigate the intersection to an
acceptable Level of Service "D" condition or wait until the improvements are
implemented by the City or other developments. Improvements made by the City
prior to the development of the subject project shall be reimbursed by the "new
development" based on a proportionate fair share costs of the facility
improvements.
4. Unsignalized intersections that currently operate less than a Level of Service "D"
condition, shall be analyzed for traffic signal and intersection improvements. If
three or more traffic signal warrants are satisfied, signal and intersection
improvements will be required as a mitigating measure for the "new development".
If at least 3 traffic signal warrants are not satisfied by the "new developments"
horizon year, the TIA shall determine if traffic signal warrants and intersection
improvements would be needed within a 5 year period after the "new
developments" horizon year. The "new development" would be required to provide
a proportionate share cost towards future traffic signal and intersection
improvements if warranted within the 5 year period.
However, if traffic signal warrants are not satisfied after a 5 year period from the
"new developments" horizon year, mitigating impacts would not be required from
the "new development" for traffic signal improvements.
Signalized intersections where the projected Level of Service condition is at "D", but
where one or more of the Level of Service conditions on the approaches falls below Level
of Service "D", mitigating measures may be required to improve the capacity and traffic
operations at the intersection. The City reserves the right to review all adverse traffic
impacts at these intersections and to determine appropriate mitigating measures.
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CITY OF OLYMPIA
TRAFFIC ANALYSIS
SLOPING SHEET
PROJECT INFORMATION
Date
Ref. No.
Proposed Use
Size (SgFt)
Location
Geographic N- Trip Generation
Distribution E- Land Use Code
S- Year of Occupancy
W- Ambient Growth
Related Projects
To be researched by consult under
approval of Olympia Development Services
Critical Intersections
1
2
3
4
5
6
7
8
9
10
This analysis must follow City of Olympia guidelines for a Traffic Impact Analysis
Project Developer
Address
Telephone
Traffic Consultant
Address
Telephone
Representative
Title
Telephone
cc: Impacted Jurisdictions -Lacey, Tumwater, Thurston County