There are two types of traffic studies that may be required: A Programmatic Traffic Assessment (PTA), or a Transportation Impact Analysis (TIA)

Programmatic Traffic Assessment 

A Programmatic Traffic Assessment may be required for Comprehensive Plan amendments and some Rezones when a proposal differs from the comp plan EIS analysis. The requirements for a PTA are similar to a TIA (see below), but on a larger scale and with the addition of on-site vehicle and pedestrian circulation information included. Please work with the Planning Manager or designee for exact scope and study area. 

Transportation Impact Analysis

A TIA is required for each development or redevelopment that would generate 27 or more person-trips during the PM peak hour (SMC 20.60.140). Person-trips may be estimated with the Transportation Impact Fee (TIF) Estimation form. When a project application is submitted, the assigned DRE will provide the final person-trip calculation to determine if a TIA is required. A TIA may also be required if the City Traffic Engineer assesses that the project will have a significant impact to the transportation network, even if the 27 person-trip threshold is not met. A TIA generally focuses on the PM peak period; however, the City Traffic Engineer or designee may require analysis of either one or more intersections/segments within the study area in addition to the PM period. 

The TIA scope is developed with the City Traffic Engineer. The following information helps provide information on typical TIA requirements, but please contact the City Traffic Engineer for additional details. The TIA will be reviewed as part of the permitting process. 

General Requirements

• Provide one (1) electronic copy in PDF format. The name of the document should reference the associated building permit number.
• The calculation of person-trips by land use can be found in the 2023 TIF Rate Study.  Ratios to convert between vehicle trips and person-trips are provided in the 2023 TIF rate study. 
  • Alternatively, an independent calculation can be used with adjustments to assumed trips.
  • Note – Vehicle trips are required to perform traffic Level of Service (LOS) analysis, and person-trips are required to calculate TIF.
• Traffic LOS analysis shall be conducted using methodology consistent with the most recent version of the Highway Capacity Manual. The City has recently generated a citywide model in Synchro/SimTraffic, which may be used for LOS analysis. Please reach out to the City Traffic Engineer for a copy to use in the analysis. Roundabout Analysis shall be performed using Sidra software per WSDOT Policy. 
  • See SMC 20.60.140 part A.1 and figure 20 of the most recent Transportation Element of the Comprehensive Plan (Shoreline Ordinance No. 975) for LOS requirements. 
• V/C ratio - See SMC 20.60.140 part A.1 and figure 20 of the Transportation Element of the Comprehensive Plan for V/C requirements. V/C ratio is calculated as segment volume / segment capacity. 
  • Segment Volume – provide traffic counts for any roadway segment within the study area.
  • Segment Capacity – Provided in this pdf.
  • A formatted excel file was created to more easily enter turning movement volumes to automatically calculate segment V/C ratios. 
• The year of completion of the project’s final phase shall be used as the horizon year. 
• The study shall be prepared by a Professional Engineer licensed in the State of Washington with a background in Traffic Analysis

Study Area

At minimum, the following should be included in the analysis: 

• Site access point(s)
• Nearest intersection(s) to arterial streets. See the Street Classification Map on our frequently requested maps page. 
• Any intersection and/or roadway segment with an expected increase of 20 PM vehicle trips
  • Coordinate with the City Traffic Engineer or designee for trip distribution. 

The City Traffic Engineer or designee may require additional intersections of concern to the study area. 

Transportation Impact Analysis Outline

The TIA outline can also be found in appendix E of the most recent Engineering Development Manual (EDM)

1. Cover Page 
   • Applicant/Permittee’s name
   • Project Title
   • Project address
   • Preparer’s contact information, signature, and Professional Engineer stamp.
2. Introduction
   • Complete project description
   • Current and proposed zoning designation 
   • Size of development such as number and type of housing units and/or gross floor area of various land uses
   • Phasing plan for complex projects
   • Project location and study area boundary
   • Executive summary of findings and mitigations, if applicable
3. Site Evaluation
   • Vehicle access and queuing
4. Traffic Impacts
   • Existing Conditions
     • Describe critical intersections and roadways within the study area.
     • Identify peak usage period(s). 
       • Typically, this will be the PM peak period, however the City Traffic Engineer or designee may require other periods to be analyzed for certain intersections/segments within the study area. 
     • Identify key pedestrian and bicycle trip generators within the study area.
     • Note any school crossings in the study area. 
     • Identify City capital projects and planned transportation improvements located in the study area.
     • Identify transportation improvements in the study area planned by other private developers or by governments or agencies other than the City.
     • Identify existing roadway volumes as well as entering and exiting volumes from the site during the PM and peak usage period(s). Existing trips shall be measured assuming full occupancy of the existing use on site. 
     • Existing LOS and queuing at intersections and applicable roadway segments in the study area. For LOS requirements, see figure 20 of the Transportation Element of the Comprehensive Master Plan
     • Existing v/c ratio for any minor arterial or principal arterial roadway segment in the study area. 
     • Description of other travel modes and facilities serving the project location within the study area. 
     • If applicable, a gap analysis, transportation network model analysis may be required at the discretion of the City Traffic Engineer.
   • Future Conditions
     • Vehicle Trip generation – using most recent ITE Trip Generation Manual
       • Alternatively, person-trips from the trip rate study can be converted to vehicle trips.
     • Reduction to ITE Vehicle Trip Generation values – See the TIF webpage for information on adjustments to trip rates. 
     • Background vehicle traffic growth – typically assumed to be 1.5%.
     • Pipeline project growth – trips due to nearby projects currently in development. 
       • Work with City Traffic Engineer or designee for projects in develop within the study area. 
     • Vehicle trip distribution 
     • Future vehicle LOS and queuing at intersections and applicable roadway segments in the study area without project volumes. 
     • Future Vehicle LOS and queuing with project volumes 
       • Any intersection that does not meet LOS minimums will require additional mitigation.
     • Future v/c ratio for any minor arterial or principal arterial roadway segment in the study area without project volumes 
     • Future v/c ratio with project volumes 
       • Any segment that does not meet V/C ratio requirements will require additional mitigation.
5. Safety
   • Document collisions within the study area boundary for the most recent three (3) years of collision data available. Collect collision data from WSDOT
   • Reference the City’s Most Recent Annual Traffic Report. For any locations within the study area that have collision reduction strategies identified, the project must assist in mitigation by either implementing the collision reduction strategy or by paying a proportional amount of the cost of mitigation to be determined by the City Traffic Engineer or designee 
   • For any intersections within the study area with permissive left turns, provide a cross-product analysis. 
     • Use exhibit 4-16 in the 2nd edition of the Signal Timing Manual and show that intersection volume cross products (vlt x vo) do not exceed thresholds listed. If cross products exceed thresholds, mitigation may be required. 
6. Parking Impacts
   • If justifying a reduction to on-site parking or implementing a parking management plan, include within the TIA here. 
7. Neighborhood Impacts
   • Depending on the project’s impact to nearby local streets, implementation of traffic calming may be required, and will be coordinated with the City Traffic Engineer or designee.
8. Traffic Impact Fee
   • If an independent Traffic Impact Fee is calculated, provide calculation table within the TIA. See the TIF webpage for further information on TIF calculation. 
     • If any exemptions are granted, please include in the TIF calculation for tracking purposes. 
   • Include SEPA mitigation fee, if project is within a SEPA Mitigation Area – see TIF webpage for further information. 
9. Conclusion 
   • Summarize project impacts and/or mitigations, including any impact fees.
10. Appendices 
    • Appendices should contain at minimum the following:
      • Site Plan
      • Collected Turning Movement Counts
      • Synchro/Sidra/Modeling Outputs – should contain at minimum the following:
        • Control Type
        • Signal Timing / phase information (if applicable)
        • LOS for each approach and intersection as a whole
        • Storage Lengths
        • Speed Limits
        • Queue Lengths
        • Vehicle Volumes 
        • Ped/Bicycle Volumes (conflicting peds)
      • Trip Generation Calculations, including reductions. 
      • Printout of SEPA mitigation calculation, if applicable