How does a collision warning system shape driver's brake response time? The influence of expectancy and automation complacency on real-life emergency braking

• Driving with collision warning system can affect BRT and could generate automation complacency.
• Collision warning system affect perception time and elaborating time, not movement time.
• Facial expression and perception time can be used to discriminate driver's expectations effect.
• Anticipatory information, previous direct experience, reliability of the device, and predictability of the hazard affect in different ways the steps of a brake reaction process.

Brake Reaction Time (BRT) is an important parameter for road safety. Previous research has shown that drivers' expectations can impact RT when facing hazardous situations, but driving with advanced driver assistance systems, can change the way BRT are considered. The interaction with a collision warning system can help faster more efficient responses, but at the same time can require a monitoring task and evaluation process that may lead to automation complacency. The aims of the present study are to test in a real-life setting whether automation compliancy can be generated by a collision warning system and what component of expectancy can impact the different tasks involved in an assisted BRT process. More specifically four component of expectancy were investigated: presence/absence of anticipatory information, previous direct experience, reliability of the device, and predictability of the hazard determined by repeated use of the warning system. Results supply indication on perception time and mental elaboration of the collision warning system alerts. In particular reliable warning quickened the decision making process, misleading warnings generated automation complacency slowing visual search for hazard detection, lack of directed experienced slowed the overall response while unexpected failure of the device lead to inattentional blindness and potential pseudo-accidents with surprise obstacle intrusion.