Abstract: A reversible roadway (contra-flow) is one in which the direction of traffic flow in one or more lanes is reversed to the opposing direction for some period of time. Reversible lanes have been widely used, especially in recent years, for the evacuation of major metropolitan regions threatened by hurricanes etc. One important problem in the practice of evacuation traffic organization is to choose right road links for contra-flow. Most research on the choice of contra-flow links does not consider the influence of intersections, which may lead to overestimation of evacuation capacity especially in congested urban road networks. An evacuation road network is abstracted as a special network with directional node-weights by considering the capacity of intersection movements as directional weights of nodes. The critical edge for increasing the maximum flow value of such network is defined as the one that can maximize the range of flow value increase by increasing its capacity. Alternative links for contra-flow can be got by searching critical edges in such network. A modified algorithm is presented to find such critical edges on the basis of the maximal capacity path algorithm for the classical maximum flow problem. A numerical example is given and the effects are tested through traffic simulation. It is shown that the results when considering the influence of intersections are more reasonable. The total evacuation time can be compressed more effectively by increasing the capacity of road links when considering the influence of intersections.

Key words: emergency traffic, choice of contra-flow links, intersection, network with directional node-weights, critical edge for increasing the maximum flow value of a network