Why did my car just do that? Explaining semi-autonomous driving actions to improve driver understanding, trust, and performance

This study explores, in the context of semi-autonomous driving, how the content of the verbalized message accompanying the car's autonomous action affects the driver's attitude and safety performance. Using a driving simulator with an auto-braking function, we tested different messages that provided advance explanation of the car's imminent autonomous action. Messages providing only "how" information describing actions (e.g., "The car is braking") led to poor driving performance, whereas "why" information describing reasoning for actions (e.g., "Obstacle ahead") was preferred by drivers and led to better driving performance. Providing both "how and why" resulted in the safest driving performance but increased negative feelings in drivers. These results suggest that, to increase overall safety, car makers need to attend not only to the design of autonomous actions but also to the right way to explain these actions to the drivers.