An Active Safety-Collision Warning Pilot in Washington State Estimated a Potential Upper Bound of Annual Total Net Benefits Between $1.1M and $2.1M Due to Prevention of Collisions with Vehicles, Pedestrians, and Bicyclists.

A Pilot Study in Spring 2016 Equipped Buses in Metro Areas Across Washington State with a Collision Avoidance Warning System (CAWS) and Extrapolated Cost Savings from the Collected Data.

Date Posted

Active Safety-Collision Warning Pilot in Washington State

Summary Information

This project, conducted under the auspices of the Washington State Transit Insurance Pool (WSTIP), involved field testing and evaluating a vision-based Collision Avoidance Warning System (CAWS) specifically developed for use on transit buses. The CAWS uses four cameras to provide coverage of blind zones where vulnerable road users may be hidden from the driver’s view:

  • a master camera attached to the center of the inside windshield
  • a camera attached to the inside windshield positioned to cover the blind zone on the left front created by the "A" pillar
  • one external forward-facing camera on each side of the bus towards the rear, to cover blind zones behind the driver.

Alerts and warnings about imminent collisions are displayed to the driver by visual indicators located on the windshield and front pillars. The CAWS provides alerts and warnings to a bus driver for the following conditions that could lead to a collision: 1) changing lanes without activating a turn signal (lane departure warning was disabled for this pilot), 2) exceeding posted speed limit, 3) monitoring headway with the vehicle leading the bus, 4) forward vehicle collision warning, and 5) pedestrian or cyclist collision warning in front of, or alongside the bus.


The first phase of this project involved equipping 38 transit buses with the CAWS. The buses traveled 352,129 miles during 23,798 operating hours from April 1, 2016 to June 30, 2016. During this period, they had no ped-bike collisions. To determine a long-term cost savings, the project monitored the number of warnings that the system issued to the group of drivers actively using the CAWS and compared this number to the number of warnings that a version of the system operating in “stealth mode” would have issued. A crash reduction factor was created based upon the increase in safe driving. The project then multiplied the percentage crash reduction by the total insurance claims per year over the previous 13 years to find monetary savings. The cost of the system was added back to find the net improvement.


  • The buses using the CAWS had 43 percent fewer aggregated pedestrian collision warnings and pedestrian detection zone alerts and 71 fewer percent forward collision warnings per 1000 miles.
  • Extrapolating out, this would lead to $13.1M reduction in vehicle claims, $6.9M reduction in pedestrian claims, a total of $20.0M due 58.5 percent potential reduction in claims.
  • Projecting forward and including system costs, the study estimated that the CAWS could reduce net costs by up to $1.1M per year in year five and $2.1M per year by year 14.
  • After the study period ended, three transit agencies (Ben Franklin, King County Metro, and Pierce Transit), decided to keep using the CAWS on their buses.
  • However, drivers often noted in the qualitative section that the system frequently produced false positives which negatively affected their perceptions about the systems’ usefulness. 
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