A Comparison of Four-Step Model and Path Flow Estimator for Forecasting Network Flow: A Case Study of Cache County in Utah

Development of alternative methodologies for travel demand modeling has become important in recent years due to the lack of resources for small and medium communities to adopt conventional four step travel models. Many researchers have proposed alternative tools of travel demand modeling for these communities. But majority of them still require large amount of data and technical sophistication. In this study, the Path Flow Estimator (PFE) is used to estimate the network traffic of Cache County. PFE estimations are based on the collected traffic counts, vehicle production and attractions of zones estimated using Institute of Transportation Engineers (ITE) trip generation rates. The daily trips of the four step model are converted into peak hour trips using a common peak hour factor. The PFE estimations are then compared with the estimations of the four-step model. The differences in vehicle trip production and attraction estimates by both models are due to the use of a common peak hour factor to reduce the daily trips of the four step model to peak hour trips. These differences got dis-aggregated spatially in the trip table estimations, leading to similar trip table estimations. The trip length frequency distributions of both models accounting for congestion have similar distribution. The average trip length estimated by PFE is 2.36 minutes more than the four-step model. Further, PFE has estimated link flows better than the four step model on the links having ground counts due the traffic counts constraint in PFE' s formulation. Low percentage root mean square errors between PFE and the four step model estimated link flows show that PFE has replicated the link flows satisfactorily. The four-step model has overestimated the link flows on Main Street due to the use of daily trips V-C ratio in the zones with high demand due to the slight overestimation of trips by ITE trip generation rates for those zones. On the screenlines identified in the original four step model also PFE has performed better than the four step ...