Institute of Transportation, MOTC

       Crashes involve powered-two-wheelers (PTWs) in Taiwan is largely attributed to the high crash-risk driving situations that arise from a mixed traffic environment and unsafe lane sharing behavior such as overtaking in different/the same lane by PTWs, yet there has been only limited research on how this behavior, in conjunction with roadway design such as lane width and number of lanes. This study seeks to investigate the effects of roadway design on PTW lane sharing behavior frequency and crash risks in an urban mixed traffic environment. A before-and-after micro level safety analysis was carried out based on evaluating the effects of lane width and number of lanes before and after the adjustment on lane sharing behavior. These behaviors were extracted from the vehicle trajectory and velocity data which captured by a microwave radar at 100 milliseconds, and also considering the time-to-collision (TTC) as the crash surrogate measure of these behaviors. In the block-based analysis, which was to investigated if the lane sharing behavior frequencies are related to roadway design, a bivariate Poisson regression model was proposed to consider the correlation between two lane sharing behaviors. The results showed that the widen of lane width and a reduction in the number of lanes from 3 lanes to 2 lanes directionally lead to the increasing overtaking in the same lane events, the less of overtaking events, and the greater the lateral position variability of PTWs. The purpose of event-level analysis was to examine what driving situations would affect the probability of a risky event. The results obtained from event-level analysis showed that the increase of the lane width results in higher crash risk; however, the driver behavior and kinematic factors such as speed, lateral distance, passing side dominated the potential of crash. Overall, roadway design adjustment was found to have a highly significant effect on PTW lane sharing behaviors frequency, but still depends on driver’s riding skill, risk perception to enhance the urban traffic safety.