Forward collision warning (FCW) alone, low-speed autonomous emergency braking (AEB), and FCW combined with AEB that operates at highway speeds reduced rear-end striking crash involvement rates by 27 percent, 43 percent, and 50 percent, respectively.
Insurance Institute for Highway Safety analysis of police-reported crash data in 22 U.S. states from 2010–2014.
Made Public Date

Effectiveness of Forward Collision Warning and Autonomous Emergency Braking Systems in Reducing Front-to-Rear Crash Rates

Summary Information

Front crash prevention systems are designed to prevent frontal crashes or lessen their severity. Most systems warn the driver when a frontal collision becomes likely and precharge the brakes to maximize their effectiveness when the driver responds. Some systems brake autonomously if the driver does not respond to the warning, and others brake autonomously at low speeds without a prior warning. Autonomous braking can reduce the severity of a crash by lowering the speed of the striking vehicle if it does not prevent the crash entirely.

Forward collision warning (FCW) was first introduced in the United States by Mercedes-Benz in 2000. Systems with autonomous emergency braking (AEB) followed, and were first offered in the United States by Acura in 2006. Systems were initially offered as optional equipment in luxury vehicles but have become more widely available in recent years. In model year 2016, 40 percent of U.S. vehicle series offered FCW systems with AEB, most as optional equipment, and an additional 21 percent offered FCW systems without AEB. Ten U.S. automakers pledged in September 2015 to make AEB standard equipment in all of their vehicles.

The purpose of this study was to evaluate the effectiveness of forward collision warning (FCW) alone, a low-speed autonomous emergency braking (AEB) system operational at speeds up to 19 mph that does not warn the driver prior to braking, and FCW with AEB that operates at higher speeds in reducing front-to-rear crashes and injuries.


Poisson regression was used to compare rates of police-reported crash involvements per insured vehicle year in 22 U.S. states during 2010-2014 between passenger vehicle models with FCW alone or with AEB and the same models where the optional systems were not purchased, controlling for other factors affecting crash risk.

Similar analyses compared rates between Volvo 2010-2012 models with a standard low-speed AEB system to those of other luxury cars and SUVs without the system.

Study vehicles were the striking vehicle in 7,490 rear-end crashes, 2,267 rear-end injury crashes, and 1,964 rear-end third-party injury crashes.


FCW alone and FCW with AEB are effective in reducing rear-end crashes, and FCW with AEB is effective in reducing rear-end injury crashes, based on the crash experiences of drivers who have purchased the optional technologies.

  • FCW alone, low-speed AEB, and FCW with AEB reduced rear-end striking crash involvement rates by 27 percent, 43 percent, and 50 percent, respectively.
  • FCW alone, low-speed AEB, and FCW with AEB reduced rates of rear-end striking crash involvements with injuries by 20 percent, 45 percent, and 56 percent, and rates of rear-end striking crash involvements with third-party injuries were reduced by 18 percent, 44 percent, and 59 percent, respectively.
  • FCW alone and low-speed AEB reduced rates of being rear struck in rear-end crashes by 13 percent and 12 percent, respectively, but FCW with AEB increased rates of rear-end struck crash involvements by 20 percent.
  • Almost 1 million U.S. police-reported rear-end crashes in 2014 and more than 400,000 injuries in such crashes could have been prevented if all vehicles were equipped with FCW and AEB that perform similarly as systems did for study vehicles.
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