Feedback with Alternate Trip Assignment Approaches in the Four-Step Model

The traditional Four-Step Model is widely used in the Transportation Planning and Forecasting Process. However, the model itself has a structural defect: it is only equilibrium in terms of Trip Assignment. Thus it is often viewed as an inadequate, partial equilibrium model. To achieve an overall equilibrium in the Transportation Planning and Forecasting Process, a feedback process can be introduced into the Four-Step Model.;The objective of this research is to incorporate different feedback methods into the traditional Four-Step Modeling process to improve model performance. The specific approach herein is to examine the relative performance of direct and averaging feedback methods, and then to investigate the convergence of this two approaches by replacing User Equilibrium trip assignment with All-or-Nothing trip assignment during each feedback loop, but not in the original four step model application. An evaluation and comparison of these methods is presented. Two measures of effectiveness, the Root-Mean-Square Error (RMSE) and Total Vehicle Hours Traveled (VHT), are employed to test the convergence and evaluate the methods.