The assignment of traffic flow to minimum cost routes through a road network is complicated by the fact that each road in the network may have a separate relationship between the flow along that road and the average speed at which it will travel. This problem, that of assignment based on such speed flow relationships, is difficult to handle in practice and most methods yield flow assignments of uncertain precision. This report presents a technique for producing assignments over congested routes and for assessing the accuracy of the result. By reiteration solutions of increasing precision can be obtained. At the same time the size of systematic errors is indicated thus enabling confidence limits to be set in economic assessments that are based on the flow assignments. The methodology can be extended to handle overloaded networks, and comparisons are drawn between this approach and the linear programming methods employed in phase III (1) of the London Transportation Study. (Author/publisher)
Abstract