Identifying factors affecting drivers' selection of unconventional outside left-turn lanes at signallised intersections

An unconventional outside left-turn lane design has been increasingly used at signallised intersections in the urban areas in China. The unconventional outside left-turn lane design allows an exclusive left-turn lane to be located to the right of through lanes. The study presented in this paper evaluated the factors that affected drivers' selection of left-turn lanes at signallised intersections where both inside and outside left-turn lanes were provided. A binary logit model was developed to quantitatively evaluate the impact of contributing factors on drivers' selection of outside left-turn lanes. It was found that the chance of a driver choosing the outside left-turn lane would increase with an increase in the traffic volume on the major street and the queue length in the inside left-turn lane; and would decrease with an increase in the distance between the upstream side street to the signallised intersection. In addition, drivers of heavy vehicles and those from the upstream right-side side streets were more likely to select outside left-turn lanes. Based on the data analysis results, a procedure was proposed to help transportation professionals determine if outside left-turn lanes were needed given traffic conditions and geometric characteristics of a signallised intersection.