Improving highway traffic performance: Merging pattern design of a departure zone after tollbooths or ETC

There are two kinds of traffic congestion at a toll plaza on a highway: Congestion in the approach zone and congestion in the departure zone, while congestion in the departure zone has received less attention. The performance improvement in the departure zone can directly reduce congestion in that area and indirectly increase traffic capacity in the approach zone by increasing the upper limit of the outflow from the departure zone. In this paper, we propose a method on merging pattern design in the departure zone after tollbooths or electronic toll collection, to determine the optimal merging patterns for the departure zones with two typical shapes (i.e., right-trapezoidal and isosceles-trapezoidal). Different traffic congestion simulations show that, for the departure zone with either right-trapezoidal or isosceles-trapezoidal, our optimal merging pattern has the largest throughput, shortest mean time delay, and smallest average number of stops per vehicle, among other possible merging patterns, in heavy traffic scenarios. The optimal merging pattern for the isosceles-trapezoidal departure zone is usually better than that for the right-trapezoidal departure zone.