Automatic Collision Avoidance Systems (ACAS) aims to help drivers to avoid accidents by alerting them to a potential collision and initiating braking. This paper assesses the safety effects of ACAS by examining driver response during emergency braking situations. A series of emergency braking tests were undertaken on a test track. Six subjects (each with at least five years driving experience) were asked to follow a special 'dummy' vehicle and drive the TRG instrumented vehicle. The dummy vehicle, a light weight trailer unit designed to withstand impacts safely, was then subjected to brake to a stop from three speed levels (60, 45 and 30 mph) with decelerations which varied between 0.65g and 0.95g. The TRG instrumented vehicle enabled detailed information to be collected on driver responses such as relative speed, spacing distance, pedal movement, speed and deceleration levels. The data analysis has showed that drivers are likely to initiate their braking before the time to collision (TTC) reaches 4 seconds. Consequently, an autonomous ACAS with a 4 seconds TTC threshold would not give warning that could help drivers reducing their response time. Moreover, headway was found to be the main safety factor that ensures drivers would avoid collision. For the covering abstract see ITRD E825082.
Abstract