The influence of alarm timing on braking response and driver trust in low speed driving

Forward collision warning systems (FCWS) have been developed to reduce collision accidents caused by driver inattention. The timing of the alarm is a crucial factor in the determination of system effectiveness and in order to achieve the potential benefits it is necessary to estimate the effects of alarm timing on driver behaviour in all driving scenarios. In this study, we focused on driver behaviour when driving at relatively low speed (30 mile/h) and investigated the effect of alarm timing and driving demand on driver braking strategy in imminent collision situations. Three kinds of alarm timing condition (early alarms, late alarms, and no alarms) and two levels of driving demands (high and low decelerations of a leading vehicle) were considered and driver response to alarms was investigated from the viewpoint of driver trust. The results support the following conclusions. Trust in early alarms is higher than that in late alarms regardless of the differences in deceleration of the leading vehicle. In situations where the leading vehicle decreases its speed rapidly, an early alarm timing induces more timely and consistent braking actions than a late alarm timing. In situations where the leading vehicle decreases its speed gently an early alarm timing is unlikely to improve driver performance. Drivers who experience late alarms tend to respond to the brakes before an alarm sounds, moreover a late alarm timing has the potential to impair driver trust due to a conflict between driver expectation and alarm performance. Finally, evidence indicating a relationship between trust and alarm timing is discussed.