Based on a business establishment commercial vehicle (CV) travel survey conducted in 2010, a series of models has been developed for intra-region commercial vehicle trips for the Triangle Region of North Carolina. However, modeling and forecasting commercial vehicle trips that have one or both ends outside the region is more challenging since commercial vehicle travel is usually substantially influenced by the economy, not only of the region studied but also of the state or even the country. To improve the modeling of internal-to-external (I-E), external-to-internal (E-I), and through (E-E) commercial vehicle trips for the region, the North Carolina Statewide Travel Model (NCSTM) was utilized and interfaced with the Triangle Regional Model (TRM). The statewide model uses nationwide and more economy-sensitive Freight Analysis Framework (FAF) data for forecasting freight-related commercial vehicle trips. Incorporating the statewide model forecasts into the regional model has shown noticeable improvements over the old approach. However, the process needed to address some critical issues when putting the two models together, since the input data and model specifications are so different between the models and reconciliation therefore had to be made to bridge the gaps, such as:
• The TRM uses a more detailed network than the NCSTM and hence has more external stations. A method was developed to allocate statewide model forecasted traffic to those stations.
• The NCSTM uses FAF3 data for long haul truck trips and Quick Response Freight Manual (QRFM) rates for short haul/local trips. The industry/employment categories used in these two sub-models are different from each other and also different from those used in the TRM. Correspondences were developed with quite a bit of effort.
• Trip rates were adjusted / synthesized based on the developed correspondences accordingly.
• To achieve reasonable trip length frequency distribution when disaggregating the NCSTM truck trip matrices, TLFD derived from the regional CV travel survey and the external station cordon survey was employed as the target in the fitting process.
This paper will document the methodology, issues encountered and resolved, and lessons learned from the interfacing work.