Interactions between automated driving systems (ADS) vehicles and conventional vehicles are likely to be different than interactions between conventional vehicles only, and these differences could have positive or negative safety consequences.

Westat supported the National Highway Traffic Safety Administration’s (NHTSA’s) efforts to investigate the potential for safety impacts when vehicles controlled by automation interact with conventional vehicles driven by people.

Westat performed the following tasks:

• A review of knowledge on ADS–conventional vehicle interactions. This included an analysis of crash scenarios that would be relevant for these interactions.
• An on-road study investigating the behaviors of drivers who find themselves in the vicinity of a vehicle identified as a self-driving vehicle as compared to a conventional vehicle. This study was conducted in traffic on limited access highways in Maryland. We measured close following and merging behavior, as well as passing drivers’ “looking” behavior and facial expressions.

The results of this project provided evidence of how the introduction of ADS vehicles on public roads is likely to affect vehicle interactions and safety outcomes. NHTSA is using the findings to

• Support its human factors automation research program
• Identify potential challenges and opportunities with regard to ADS–conventional vehicle interaction
• Prioritize future research