This study, which was designed to provide guidance on the accuracy and usefulness of various projection techniques for various levels of aggregation and periods of time, focused on two areas of research: the sensitivity of the transportation planning process, particularly trip generation, to variation in input socioeconomic and demographic variables; and review and evaluation of methodology for producing study area level projections either on the basis of other projections or independently. The results of the study are presented, conclusions are drawn and recommendations are made. It was found that trip generation is extremely sensitive to population projections, but much less sensitive to projections of numbers of households (or household size) if population is controlled. Given population and household size, household auto ownership and income substantially enhance the explanation of variation in household trip generation. Socioeconomic and demographic data also play a strong role in mode choice models. For planners with adequate resources, the cohort-component projection models are superior. For the planner with limited resources, the best procedure would be to "step down" from national, state, or multicounty projections prepared using complex techniques. Other major conclusions are also presented.
Abstract