Improvement of Evaluation Indices for Rear-End Collision Risk

There are various kinds of indices to evaluate collision risk against forward obstacles, which are used to determine the timing of collision warning provision in forward obstacle collision warning systems (FCWSs) and advanced emergency braking systems. A previous study proposed a deceleration for collision avoidance (DCA) method, which can evaluate a collision risk more precisely than other conventional indices. However, the calculation process of DCA assumed that a following vehicle (FV) performs a uniform motion within a driver's constant reaction time. The assumption causes underestimation of collision risk when the FV accelerates and overestimation when it decelerates. Consequently, this paper shows a detailed calculation process of an improved DCA based on an expanded assumption that the FV maintains a uniformly accelerated motion within the reaction time. Moreover, stimulus-response experiments were conducted to measure the driver's reaction time when he/she adjusts the brake pedal depression. Numerical simulations, where DCA is used for the FCWS, were performed to show that the improved DCA (with a new setting for the driver reaction time) describes the collision risk more properly compared to the conventional DCA.