Third Brake Light Is No Third Wheel

A third brake light on cars saves lives, property and money.

Flashing lights, honking horns, meandering pedestrians, fighting kids in the back seat -- a driver's attention is spread thin, which is one reason why car accidents are so commonplace. In 1974, psychologist John Voevodsky tested a small, inexpensive gadget that would eventually make U.S. highways much safer. The gadget was a third brake light, mounted in the base of rear windshields so that when drivers pressed their brakes, a triangle of light warned following drivers to slow down. To test whether such a small addition would make a significant difference, Voevodsky equipped 343 San Francisco taxicabs with the third brake light and left 160 taxis with no additional light as a control group. Taxi dispatchers then randomly assigned taxi drivers to taxis with or without the third light, regardless of drivers' expressed preferences. At the end of a 10-month experiment, taxis with a third brake light had suffered 60.6% fewer rear-end collisions than had the control-group taxis. Additionally, drivers of taxis with the third brake light that were struck in the rear by other vehicles were injured 61.1% less often than were drivers of taxis without the light, and repairs to all taxis with the light cost 61.8% less than did repairs to taxis without the light.

This is the first published study showing that a third brake light reduces automobile accidents.

The National Highway Traffic Safety Administration (NHTSA) repeated Voevodsky's experiment on a larger scale, and concluded that Center High Mounted Stop Lamps (CHMSLs) reduce accidents and injuries. As a result, the NHTSA now requires all new cars (since 1986) and all new light trucks (since 1994) to have a third brake light. To see just how well the CHMSLs worked, the NHTSA has charted police-reported crash data from eight states, and has found that CHMSLs reduce rear impacts by 4.3%. Although less dramatic than the original findings, this finding means that since the CHMSL became standard equipment, there have been about 200,000 fewer crashes, 60,000 fewer injuries, and over $600 million in property damage saved every year - not to mention the lives saved. To put that in dollars and cents: for every dollar spent on manufacturing and installing the third brake light, $3.18 is saved.