ABSTRACT
Much of the work done on the selection of primary design loads for bridges has been concerned with the identification of a single heavy vehicle, for example, a truck with a specified return interval. This work needs to be extended in two ways: (a) all modern bridges carry at least two lanes of traffic, and truck loads in parallel lanes need to be considered; (b) in long span bridges, there are also significant effects from the presence of succeeding vehicles in each lane.
