The effectiveness of center high mounted stop lamps - a preliminary evaluation

a nationally representative data set. The involvement rate in rear impacts for model year 1986 cars (all CHMSL equipped) is compared to 1985 cars (mostly without the lamps). CHMSL reduced the likelihood of being struck in the rear while braking by a statistically significant 22 percent. (In the NASS data, CHMSL reduced rear impacts of all types by 15 percent; since earlier studies indicated that two thirds of all rear impacts involve braking by the struck car, the 15 percent overall reduction is equivalent to a 22 percent reduction of rear impacts while braking.) The data also suggest that CHMSL may be especially useful in preventing chain collisions involving three or more vehicles. All effectiveness estimates have to be considered preliminary and may change in follow-up studies based on larger accident samples.