Abstract
Advanced driver assistance system (ADAS) has been expanding recently. In order to enhance the effectiveness of ADAS with drivers’ acceptance, it is important to consider how the system can assist drivers without disturbing their maneuvers. For example, when an ADAS assists a driver in avoiding rear-end collision, the system will be acceptable without nuisance if it can estimate his/her normal brake/steer avoidance maneuver timing based on the perceptual proximity risk. In this study, we aimed to develop an index of the driver's perceptual risk of longitudinal direction. First, we introduced a model with which a driver estimates proximity risk based on two kinds of perception derived from previous studies: kinematic perception to approach a lead vehicle and dynamic perception when the lead vehicle decelerates. Then, we proposed an index reflecting these kinds of perception. The index is formulated as "perceptual relative velocity" divided by "perceptual distance." Both elements are corrected from their physical value so as to reflect their perceptual magnitude. The perceptual distance is the exponent of the distance between the subject vehicle and the lead vehicle. The perceptual relative velocity is the velocity difference of these two vehicles corrected by the subject vehicle's velocity and their relative acceleration. We tested the model with brake avoidance maneuvers on test track. It was found that drivers' brake timings were well matched to the model; they braked when the proposed index reached a certain threshold. Thus, the index, called PRE, was confirmed to be able to measure driver's perceptual risk estimate. Since the PRE can describe perceptual proximity risk, it is natural to consider that it also can predict steer avoidance maneuver timing, although the timing, i.e., the parameters of the PRE, may be different from those for brake. We again tested with actual vehicles and found that the PRE also matches to steer avoidance timing, and as we expected, the parameters were different from those for brake. Finally, the PRE was compared with such indices as TTC, THW, Risk Perception (RP), and KdB_c, and it was shown that the PRE is a comprehensive and enhanced model of those indices.
Keywords: Visual Perception, Preventive Safety, Collision Avoidance