Rear impact crashes are the most frequent type of bus accidents. Transit buses are particularly susceptible to rear impact collisions because of their frequent stops, which often occur in traffic lanes. The majority of bus collisions occur while the bus is decelerating or stopped. The preponderance of crashes occur with buses stopped during daylight hours, in good weather conditions, while traversing a straight path, and with the striking vehicle attempting no avoidance or corrective action.

To respond to this surprising set of crash conditions, General Dynamics, in partnership with the Ann Arbor Transit Authority (AATA), developed a Rear-Impact Collision Warning System (RICWS) based on our premise that following drivers were either being distracted or simply not paying attention. To determine the following drivers’ behaviors behind transit buses, General Dynamics first conducted a series of field collections using a recording system, digital video, and a laser front-end sensor mounted on the rear of an AATA bus in service. These “behaviors” were then used to build decision logic to determine when a dangerous situation required mitigation or countermeasures.

General Dynamics then developed a visual warning system. Tests concluded that a light bar with a specific moving light pattern was effective in attracting a distracted driver’s attention. This light bar was added to the RICWS and was turned on once a following vehicle committed dangerously aggressive closing behavior toward the rear of the test bus. Three warning algorithms were field tested, each with different parameters defining ‘aggressive closing behavior.’

Both Phase II and Phase III of this program produced informative results regarding typical following driver behavior behind buses. The light bar proved effective in modifying following drivers’ behavior (with all three algorithms). A set of comprehensive RICWS specifications were generated as well as future commercialization steps for the system.