Evaluation of a Transit Bus Collision Avoidance Warning System in Virginia

About the report:

Although professional bus operators receive extensive safety training, even a safe operator can become distracted at times or can lose sight of a vulnerable road user in one of the vehicle’s blind spots. In 2017, the Virginia Department of Rail and Public Transportation (DRPT) initiated a demonstration project to plan, implement, and evaluate a transit bus collision avoidance warning system (CAWS) on up to 50 buses.  The Mobileye® Shield+ Advanced Driver Assistance System (referred to here as “the CAWS”) uses kinematic sensors and multiple external camera sensors to provide visual and/or audio alerts in various categories: daytime pedestrian/bicyclist detection, warnings for exceeding the speed limit, lane departure warnings, and headway monitoring/forward collision warnings. 

The purpose of this study was to conduct an evaluation of the CAWS demonstration project in terms of system effectiveness and bus operator acceptance. The scope was limited to agencies participating in the demonstration project. 

The study found that the benefits of the CAWS in a transit operating environment were mixed: the driving performance of operators, as measured by event rates in the CAWS data, generally improved after they began receiving system alerts. However, in surveys, operators had mixed reactions to the system, with 75% of respondents saying that they often or sometimes noticed false alarms and 76% of respondents saying that the system was very or somewhat distracting.  At the same time, 70% of respondents said the system was very or somewhat helpful.  These results align with findings from previous studies in that the CAWS improved safety surrogates yet was unpopular with many operators.  Thus, transit and roadway agencies should exercise caution when using CAWS data for decision-making.

The study recommends that DRPT (1) identify ways to support transit agencies that are interested in deploying bus CAWS technology, and (2) monitor bus CAWS technology as it continues to develop.  Implementing these recommendations will maximize the value of state and local technology investments by helping individual transit agencies achieve the safety benefits of CAWS while mitigating and managing the challenges. It will also position DRPT to make investments in CAWS technology when its benefits more clearly outweigh its challenges.

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