Trucks in the traffic assignment process

This paper attempts to calculate the impact of heavy trucks on highway capacity in order to determine the necessity of or the type of policy for separating trucks from cars in urban areas. There are various means of acheiving this separation. For example, certain highways and parkways exclude trucks altogether. Then there are structures (e.g. overpasses and underpasses) whose very physical characteristics bar vehicles over a given height or weight. Conversely, there are routes whose signing encourages through truck travel. The calculations of the impact of heavy trucks have yielded the following conclusions: separated but concurrent assignment of the truck origin-destination matrix over the highway network and retention of the link truck volumes is desirable for many subregional and neighborhood planning problems; provision for a truck network designation is desirable so that truck routes or truck prohibitions or both can be considered in the assignment process; as a minimum, trucks should be divided into light or auto-like trucks and heavy trucks; even a small proportion of trucks in the traffic stream can result in substantial reduction in street capacity (this capacity reduction, however, is not a simple linear reduction proportional to the percentage of trucks in the vehicle stream); and the reduction in capacity from trucks in the traffic stream can be represented by a straightforward algorithm that weights trucks differentially according to their proportion in the traffic stream.