Observations and Analysis of the Lane Changing Chain Reaction Behavior at Two Expressway Merge Bottlenecks in Shanghai

Through numerous field observations at two expressway merge bottlenecks, this paper studied a special lane changing behavior, lane changing chain reaction (LCCR), which is defined as the back-to-back lane changing behaviors of one vehicle leads to others that are induced by the first lane changing maneuver and results in the driving routes and/or velocities of successive vehicles are greatly disturbed. The detailed maneuver processes and characteristics of LCCR were described first. And then 90 sets of LCCR, 292 sets of isolated lane changing (ILC) and 100 sets of lane changing without chain reaction (LCWCR) empirical data were collected by extracting trajectories from lane changing vehicles, as well as each adjacent vehicle. Some descriptive parameters were investigated to analyze the characteristics of LCCR and through comparing the data of ILC with which of LCCR we found that LCCR has the following features: (a) it happens more often at the end half of the bottleneck; (b) most LCCR cases change lane from acceleration lane and all the lane changing directions are from right side lane to left side lane; (c) the distribution of velocity of LCCR vehicles has two peaks; (d) the main LC type is forced lane changing. Compared with ILC, the LCCR pose more disruptive influences on the traffic flow, which can cause the occurrences of rapid breakdown at merge bottlenecks. Thus, the binary Logit choice model of LCCR was established to analyze what kinds of parameters may have significant effect in inducing LCCR. The results show that the LC type, the time headway between putative lead and lag vehicle and three types of speed difference are the key factors. The research can be used to reduce or prevent the occurrence of LCCR and develop detailed analytical and/or simulation models to describe LCCR behavior.