Characteristics of rear-end crashes involving passenger vehicles with automatic emergency braking

August 2019

Objectives: Automatic emergency braking (AEB) is a proven effective countermeasure for preventing front-to-rear crashes, but it has not yet fully lived up to its estimated potential. This study identified the types of rear-end crashes in which striking vehicles with AEB are overrepresented to determine if the system is more effective in some situations than others, so that additional opportunities for increasing AEB effectiveness might be explored. Methods: Rear-end crash involvements were extracted from 23 U.S. states during 2009–2016 for striking passenger vehicles with and without AEB among models where the system was optional. Logistic regression was used to examine the odds that rear-end crashes with various characteristics involved a striking vehicle with AEB, controlling for driver and vehicle features. Results: Striking vehicles were significantly more likely to have AEB in crashes where the striking vehicle was turning relative to when it was moving straight (OR=2.35, 95% CI 1.76, 3.13); when the struck vehicle was turning (OR=1.66, 95% CI 1.25, 2.21) or changing lanes (OR=2.05, 95% CI 1.13, 3.72) relative to when it was slowing or stopped; when the struck vehicle was not a passenger vehicle or was a special use vehicle relative to a car (OR=1.61, 95% CI 1.01, 2.55); on snowy or icy roads relative to dry roads (OR=1.83, 95% CI 1.16, 2.86); or on roads with speed limits of 70+ mph relative to those with 40–45 mph speed limits (OR=1.49, 95% CI 1.10, 2.03). Overall, 25.3% of crashes where the striking vehicle had AEB had at least one of these overrepresented characteristics, compared with 15.9% of strikes by vehicles without AEB. Conclusions: The typical rear-end crash occurs when two passenger vehicles are proceeding in line, on dry road, and at lower speeds. Because atypical crash circumstances are overrepresented among the rear-end crashes by striking vehicles with AEB, it appears that the system is doing a better job of preventing the more typical crash scenario. Consumer information testing programs of AEB use a test configuration that models the typical rear-end crash type. Testing programs promoting good AEB performance in crash circumstances where vehicles with AEB are overrepresented could guide future development of AEB systems that perform well in these additional rear-end collision scenarios.