Evaluation of models to forecast external-external trip percentages

The main difficulty in forecasting traffic volumes along a rural bypass is identifying the external traffic, both traffic entering the town from outside and traffic continuing through the town to an ultimate destination. Three methods exist for determining the percentage of external traffic destined for town, external-internal, or through town, external-external: A comprehensive origin-destination study, cordon line origin-destination study, or a regression equation. The objective of this paper is to examine the possibility of using different techniques, based on spatial economic models to determine the traffic percentages. This project will use three different models to determine the activity base for the city of Waverly, Iowa, and compare the models with the results given by the regression equation and a cordon line origin-destination study performed in the 1970s. This paper demonstrates that Huff's probability contour model performs well for the case study and recommends that this model be used in the future to provide estimates that incorporate a community's economic relationship to neighboring towns.