Abstract
A simple statewide truck-travel demand model for Wisconsin was developed using only readily available data, including a small amount of data from origin-destination travel surveys (O-D) and fairly extensive truck-classification count data. A simple trip-rate trip-generation model based on zonal population was used to estimate the initial internal trip productions and attractions. Despite the small amount of O-D survey data that were available, gravity-model friction-factor curves were developed for three trip types. The calibrated gravity models produced trip tables that were good matches for the O-D survey data. The calibrated gravity models were then used as the modeling framework for the adjustment of zonal productions and attractions by selected-link-based (SELINK) analysis. SELINK adjustment factors were computed for all zones with trips on one or more of the selected links. The adjustments were made so that the ratio of the actual volume for the selected link (ground count) to the total assigned volume approached 1 for all selected links. The SELINK analysis produced a calibrated model after only three iterations when either 16 or 32 selected links were used statewide for the calibration. The overall accuracy of the calibrated model was measured by using classification count data for 154 locations around the state. The model provided a good fit based on a wide variety of measures, including percent root-mean-square error and comparisons for screenlines, functional class, areas, and vehicle kilometers traveled.
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