an equilibrium model of bus and car travel over a road network

a new model of traffic flow and travel demand over a congested network is described. all roads are subject to different speed and flow relations, and the travellers by bus and car are able to take advantage of any better routes for their journey that they can find. the pattern of travel movements produced by this process is an equilibrium distribution where any change in cost, speed, or time over any part of the network will affect the whole system and the demand for travel between all the points on the network. a technique of general applicability has been found to determine these patterns of flow and demand with a high degree of consistency for even very small charges - or other changes - applied: it is also shown that the more conventional sequence of gravity model assignment of flow, which produces stable results after several repetitions, can produce incorrect results. the technique is presented through the example of road pricing applied to road movements over a network: the importance of obtaining a unique equilibrium, the assignment improvements, and the effects on car and bus demand and movements are all demonstrated. (a).