In Snohomish County, Washington State, implementation of a transit signal priority system on two test corridors reduced average transit corridor travel time by 4.9 percent, and had insignificant negative impacts on local cross street traffic.

15 June 2007
Snohomish County,Washington,United States

Summary Information

Transit signal priority (TSP) is an operational strategy that facilitates the movements of in-service transit vehicles through signalized intersections. Since delays incurred by transit vehicles at signalized intersections typically account for 10 to 20 percent of transit vehicle running times, TSP promotes transit utilization through improving service reliability. By reducing the waiting time of transit vehicles at intersections, TSP can reduce transit delay and travel time, thereby increasing the quality of service. The South Snohomish Regional Transit Signal Priority (SS-RTSP) project was implemented at 17 intersections over two phases, and evaluation study was performed and the report was completed in June, 2007. The study quantitatively evaluated impacts of the system on both transit and local traffic operations based on a large amount of field observed traffic data and real-world traffic control settings.

Several measures of effectiveness were assessed to provide a comprehensive evaluation. To obtain accurate transit travel time data, in-vehicle GPS data loggers were used to record vehicle locations periodically. Traffic queue length data and signal cycle failure data were collected manually from video images and the frequency of TSP calls were calculated from the logged requests from transit vehicles. Using the field-observed data, MOEs for average person delay and vehicle delays and stops were determined using a microsimulation traffic model.


Evaluation results showed:
  • the SS-RTSP system reduced transit corridor travel time by approximately 4.9 percent.
  • decreased delay by approximately 336,766 person-hours per year for peak-hour travel.
  • insignificant negative impacts to local traffic on cross streets.
  • the overall person-delay saved by the SS-RTSP system was significant.

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Comprehensive Evaluation on Transit Signal Priority System Impacts Using Field Observed Traffic Data

Author: Wang, Yinhai, et al.

Published By: University of Washington

Source Date: 15 June 2007

Other Reference Number: TNW2007-06



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Benefit ID: 2008-00538