Abstract
Center High Mounted Stop Lamps (CHMSL) have been standard equipment on all new passenger cars sold in the United States since model year 1986 and all new light trucks since model year 1994, as required by Federal Motor Vehicle Safety Standard 108. The purpose of CHMSL is to safeguard a car or light truck from being struck in the rear by another vehicle. When brakes are applied, the CHMSL warns drivers of following vehicles that they must slow down. This report tracks the effectiveness of CHMSL, year by year, from 1986 through 1995. The statistical analyses are based on police-reported crash files from eight States. It was found that:
* The lamps were most effective in the early years. In 1987, CHMSL reduced rear impact crashes by 8.5 percent (confidence bounds 6.1 to 10.9 percent).
*Effectiveness declined in 1988 and 1989, but then leveled off. During 1989-95, CHMSL reduced rear impact crashes by 4.3 percent (confidence bounds 2.9 to 5.8 percent). This is the long-term effectiveness of the lamps.
*The effectiveness of CHMSL in light trucks is about the same as in passenger cars.
*At the long-term effectiveness level of 4.3 percent, when all cars and light trucks on the road have CHMSL, the lamps will prevent 92,000-137,000 police-reported crashes, 58,000-70,000 nonfatal injuries, and $655,000,000 (in 1994 dollars) in property damage per year.
*The annual consumer cost of CHMSL in cars and light trucks sold in the United States is close to $206,000,000 (in 1994 dollars).
*Even though the effectiveness of CHMSL has declined from its initial levels, the lamps are and will continue to be highly cost-effective safety devices.
