OBJECTIVE: Although partial driving automation 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). 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 the limited-access roads where they are designed to be used 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. Rear-end crash rates were 26% lower on limited-access roads and 43% lower on roads with speed limits ≤ 35 mph for Nissan Rogues with ProPILOT Assist than for those with AEB alone. Similarly, lane departure crash rates were 25% lower for Nissan Rogues with ProPILOT Assist compared with those with LDP alone on limited-access roads, but were 31% lower on roads with speed limits ≤ 35 mph and 43% lower on limited-access roads in the dark. 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 and that vehicles with it generally had better headlights than those unequipped. DISCUSSION: There is no convincing evidence that partial driving automation is a safety system that is preventing crashes in the real world. Research incorporating system use will be key to understanding safety effects. Considering that drivers have been documented misusing these systems, 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.