How to measure the influence of regional congestion to urban traffic networks

Let G(V, E) denote an undirected traffic network, some incident edges E´ may be blocked in a point, we define such incident roads blocked as a regional congestion, and present a parameter, regional congestion factor (RCF for short) that is the ratio of the total length from the root node to the rest of the each node in the shortest paths tree rooted at any node in G - E´ to the total length from the root node to the rest of the each node in the shortest paths tree rooted at any node in G, to measure the influence caused by the regional congestion, and show that this problem can be solved in O(n³) time, where n denote the number of nodes in the graph. An application of the RCF for urban traffic networks is shown.