Why do drivers brake later than AEB in rear-end collisions? An analysis based on drive recorder videos

Rear-end collisions are among the most common crash types in Japan. However, due to their relatively low fatality and injury severity, research on them remains limited. Although previous studies have shown the effectiveness of autonomous emergency braking (AEB), further studies is needed to improve understanding of driver-related factors and enhance system performance to reduce collision risk. This study investigated the effectiveness of AEB and explored factors contributing to braking delays by reconstructing 52 real-world taxi collisions exceeding 10 km/h using PC-Crash. Simulations were conducted with time-to-collision (TTC) and TTC_2nd-based (considering relative deceleration) AEB to evaluate collision-avoidance performance. Additionally, a decision tree was used to examine environmental, vehicular, and human factors affecting the time difference between driver-initiated braking and AEB activation. The result indicates that AEB installed in taxis effectively reduced rear-end collisions. TTC_2nd-based AEB could avoid more collisions involving decelerating lead vehicles. Reducing AEB delay times could further enhance prevention. However, the AEB simulation showed limited effectiveness in collisions involving high speeds, wet roads, or sudden deceleration of the lead vehicle. Moreover, the primary reason drivers braked later than the simulated AEB was their failure to maintain a forward gaze before collisions. Drivers were more likely to divert their gaze from forward driving-related areas in non-critical situations, such as low-speed driving or red traffic signals ahead. This study provides quantitative insights into human factors and AEB technology, which may inform the optimization of AEB systems and the development of driver monitoring systems, contributing to collision prevention and traffic safety.