Traffic congestion characteristics under the combined bottlenecks of an on-ramp and a lane-reduction

Studying on the generating and propagation of traffic congestions at expressway intersection, coexistence with on-ramp and lane-reduction, is challenging. It needs to figure out distinct driving behaviors of vehicles passing through different sections of the scenario, i.e., on-ramp driving zone, prompting zone, lane reduction zone, transition zone and merging zone. Also, it requires depicting the different driving patterns for trucks and cars according to road markings and drivers’ different characters. To deal with these problems, we propose a multi-lane cellular automaton traffic model, coping with the complicated traffic system including a multi-lane main road, a two-lane on-ramp and a lane-reduction area. Through numerical simulation, it is found that congestions usually occur initially at the transition zone of the on-ramp, and then propagate upstream to the entrance of the on-ramp, and also have negative effects on the traffic flow downstream, resulting in decline of traffic flows in the merging zone. Consequently, the traffic capacity in the transition zone dominates the capacity of the whole on-ramp section completely. From the perspective of traffic optimization, the strategy is proposed by shortening the length of the transition zone, and the suitable length is recommended. The study results may provide theoretical guidance for alleviating traffic congestions on expressways with on-ramp and lane-reduction area.