Observations and Analysis of Multistep-Approach Lane Changes at Expressway Merge Bottlenecks in Shanghai, China

One major cause of accidents at signalized intersections is vehicles running the red light. To discourage red light running, many authorities have installed red light cameras. From numerous field observations at two expressway merge bottlenecks, this paper identifies and studies a peculiar type of lane change, referred to as the multistep-approach lane change (MALC). The characteristics and detailed maneuvers of the MALC are first described and compared with three traditional types of lane changes (normal, cooperative, and forced). Next, descriptive parameters, such as the lane-changing duration and velocity and the number of affected vehicles, are investigated and analyzed during the transline ride (TLR) period. The parameters are taken from 132 sets of vehicle trajectory data collected at two merge bottlenecks in Shanghai, China. Significant differences are found between the MALC and traditional lane changes: the MALC takes longer to complete (10 s on average), involves lower lane-changing velocity (15 km/h on average during the TLR period), and affects more vehicles (six vehicles on average). As such, the MALC poses more disruptive influences on the traffic flow and could explain the occurrences of rapid drops in capacity at expressway merge bottlenecks.