Risk-Taking Behavior of Left-Turners in Gap Acceptance and Its Effects on Capacity Estimation at Signalized Intersections

The capacity of signalized intersections with a permissive left-turn phase is influenced significantly by the gap acceptance of left-turners. Left-turners' perception of risk when they are deciding whether to accept a gap is of great importance for understanding such driver behavior and for developing countermeasures to improve intersections. This study's objective was thus to model the tradeoff relationship between the perceived risk and the time-saving benefit in gap acceptance for left-turners in China. In the proposed model, the perceived risk was measured by the postencroachment time of the left-turning vehicle and of the gap-ending through vehicle at the conflict; the time-saving benefit was indicated by the potential time to wait for the next acceptable gap. A gap acceptance model that incorporated both variables was then developed and validated by using data collected at two intersections in Shanghai. The acceptable risk level of left-turners could then be defined as the ratio of the estimated model coefficients of those two variables. Results indicated that the wait time significantly affected the gap acceptance and the critical gap decreased as the acceptable risk level rose. In addition, the acceptable risk level was found to be approximately 60 at the observed intersections. With the results, impacts of the acceptable risk level on the capacity of permissive left-turn traffic were investigated through a numerical study. The findings revealed that the capacity of permissive left-turn traffic could be stochastic in nature rather than constant because of random traffic flow characteristics as well as different risk perceptions of drivers.