A before-and-after study found that transit patrons experienced a smoother and more comfortable ride when a transit signal priority system was implemented in Seattle, Washington.

January 2002
Seattle,Washington,United States

Summary Information

This study evaluated the impacts of transit signal priority (TSP) on traffic operations based on literature research and testimonial interviews with ten traffic engineers and planners at several state agencies. The goal of this study was to compare various TSP options and provide deployment guidelines to assist transportation agencies in deploying viable signal control strategies. Both quantitative and qualitative data were provided as well some high-level system cost information.


In the spring of 2000, the King County DOT implemented a 2.1 mile signal priority system on Rainier Avenue. The system used in-vehicle radio frequency transponders, roadside antennas, and transit priority request generators. The system was designed to control signal timings according to the following logic:
  • Approaching priority vehicles were granted extended green intervals and shortened red displays; however, signal coordination between intersections had to be maintained, and the phase cycles for adjacent traffic could not be skipped.

Major findings of the study showed intersection delay was reduced by an average of 13 percent (2.3 seconds per vehicle) during the AM peak period. In addition, minor traffic movements on side streets, and in left turn lanes off the main street showed intersection delay reductions of 3 percent (0.9 seconds per vehicle). During the midday peak, intersection delay increased slightly; however, level-of-service remained the same.

In general, before and after studies conducted by King County Metro found transit patrons experienced a smoother and more comfortable ride.

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Effectiveness of Bus Signal Priority: Final Report

Author: Chada, Shireen and Robert Newland

Published By: Florida DOT and the U.S. DOT

Prepared by the University of South Florida for the Florida DOT and U.S. DOT

Source Date: January 2002

EDL Number: 13651

Other Reference Number: Report No. CTR-416-04



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Benefit of the Month for October, 2003 !

Typical Deployment Locations

Metropolitan Areas


bus priority, traffic signals, TSP

Benefit ID: 2002-00232