The purpose of this report was to update the Arizona highway cost allocation study and to evaluate the alternative of using the new Federal Highway Administration (FHWA) cost allocation model as a replacement. The update revealed that the repeal of Arizona's weight-distance tax has led to a decrease in the payments made by the largest vehicles. As a result, these vehicles are now projected to pay less than their full cost responsibility over the 1999 through 2003 program years. Meanwhile, lighter vehicles will continue to pay more than their full cost responsibility over this same time period. Efforts to use the new FHWA cost allocation model were thwarted by the requirement for data inputs that are not readily available. This data requirement argues against using this new model.