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 car accidents are so commonplace. In 1974, psychologist John Voevodsky, PhD, 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 percent 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 percent less often than were drivers of taxis without the light, and repairs to all taxis with the light cost 61.8 percent less than did repairs to taxis without the light.


Distracted driving killed more than 3,300 people and injured 421,000 in 2012, according to U.S. government figures. A third brake light provides an extra signal to distracted drivers — and studies confirm that it reduces automobile accidents.

Practical Application

The National Highway Traffic Safety Administration (NHTSA) repeated Voevodsky's experiment on a larger scale, and concluded that center high mounted stop lamps, as the government calls them, reduce accidents and injuries. As a result, in 1986, NHTSA began requiring all new cars to have a third brake light. The agency extended that requirement to all new light trucks in 1994.

To see just how well the third brake lights worked, NHTSA charted police-reported crash data from eight states, and found that these lights reduced rear impacts by 4.3 percent. Although less dramatic than the original findings, this means that since the lights became standard equipment, there have been about 200,000 fewer crashes, 60,000 fewer injuries, and more than $600 million in property damage saved every year — not to mention lives saved.

More recently, researchers are turning their attention to the question of whether new light-emitting diode (LED) brake lights may be more effective than older incandescent bulbs at preventing rear-end collisions. Preliminary data suggest that LED lights may reduce crashes.

Cited Research

Voevodsky, J. (1974). Evaluation of a deceleration warning light for reducing rear-end automobile collisions.  Journal of Applied Psychology, 59,  270-273.

Greenwell, N.K. (2013, February). Effectiveness of LED stop lamps for reducing rear-end crashes: Analyses of state crash data. (Report No. DOT HS 811 712). Washington, DC: National Highway Traffic Safety Administration.

American Psychological Association, March 2014