Convenience or safety system? Crash rates of vehicles equipped with partial driving automation

July 2024

Objective: Partial driving automation assists drivers by providing sustained support of steering, speed, and headway. Although these systems are usually discussed as convenience features, consumers sometimes consider them to be safety features. The goal of this study was to assess if partial driving automation reduces rear-end and lane departure crashes beyond safety systems like automatic emergency braking (AEB) and lane departure prevention (LDP), on the limited-access roads and highways where they are designed to be used. Methods: Analyses examined crash rates of model year 2017–2019 Nissan Rogues and model year 2013–2017 BMW vehicles. Negative binomial regression was used to assess the association of Nissan’s partial driving automation system, ProPILOT Assist, and BMW’s system, Driving Assistant Plus, with police-reported rear-end and lane departure crash rates on limited-access roads per vehicle mile traveled. Crash rates were also examined on roads with speed limits of <= 35 mph, where the systems were expected to have limited functionality and not be used much. Results: Equipment with BMW’s Driving Assistant Plus was not associated with significantly lower crash rates than equipment with LDP alone. Crash rates were lower on limited-access roads for Nissan Rogues with ProPILOT Assist than for those with LDP or AEB alone, but these effects persisted on roads with speed limits <= 35 mph. This brings into question if the lower crash rates associated with ProPILOT Assist can be attributed to use of the system, given that it would be activated infrequently on residential roads. Discussion: There is no convincing evidence that partial driving automation is a safety system that is preventing crashes in the real world. Considering that drivers have been documented misusing these systems, partial driving automation needs to be thought of as a convenience feature and not a safety feature until there is strong support otherwise. Designing partial driving automation with robust safeguards to deter misuse will be crucial to minimizing the possibility that the systems will inadvertently increase crash risk.