Rear-End Collisions Reduced: A Large-Scale Experiment under Natural Conditions

A deceleration warning light system installed on taxicabs in San Francisco for 12.3 million miles of normal on-road driving reduced the rear-end collision rate by 60.6% compared to the rate for a concurrent control group of cabs which traveled 7.2 million miles. Comparing the experimental group with the concurrent control group revealed that the warning light prevented 5.4 collisions per million miles, 1.02 cab driver injuries per million miles, and $643 of taxicab damage per million miles. An amber light was center mounted on the rear of several hundred taxicabs and was designed to communicate information about the taxi's deceleration to following drivers.