FAST-RISE BRAKE LAMP AS A COLLISION-PREVENTION DEVICE

Conventional tungsten-filament brake lamps have a relatively slow rise time. It takes approximately 250 ms for them to reach 90% of their asymptotic luminous intensity. This slowness of response can cause important delays of warning information to following drivers. We have designed a simple and relatively inexpensive circuit that produces a faster warning signal using a conventional lamp. As we have reported previously, this device reduces reaction times to the onset of brake lamps by about 115 ms. The present study evaluated the benefits of a 115 ms reduction in driver brake reaction time. Two approaches were used. In the first approach we calculated the reductions in effective stopping distance assuming a range of initial speeds. The results indicate, for example, that if the initial speed is 100 km/h, the reduction in the effective stopping distance is 3.2 m. In the second approach we calculated the reductions in the proportions of very long reaction times, assuming a normal distribution of reaction times that is shifted by 115 ms. For the distribution without the device we assumed a mean of 1.25 s and a standard deviation of 0.46 s. The results indicate, for example, that decreasing the mean by 115 ms yields a 55% reduction in the frequency of reaction times that are longer than 2.5 s.