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58 The literature review found that there is a considerable body of research associated with developing new methods for ana- lyzing the transportation issues associated with freight. Those methods are suitable for addressing a variety of topics of con- cern to public decisionmakers. Those models can be classified according to a framework and that classification can be applied to those models used by both the public and private sectors. The most well-developed applications in support of publicâ sector decisions were time series and commodity-based mod- els, with a growing interest in, and application of, network and microsimulation models. A survey of staff supporting publicâ sector decisionmakers found a general satisfaction with the types of models that are available, but a general concern about the availability and quality of data that can support public decisionmaking for freight policies, programs, and projects. The research topics pursued focus on the use of publicly avail- able or low-cost data that can support the improvement of the models used in freight forecasting and analysis. ⢠Research into the use of low-cost GPS data for trucks, as available, from subscribers to commercial monitoring services, found that these data can be easily processed to improve the understanding of where trucks stop, and to identify the connections between those truck stops. Both the interchange of trips between land uses and the average characteristics by trip were found to be similar among four observed metropolitan areas. ⢠Research in the use of publicly available truck classification data together with publicly available commodity flow data, as assigned to a highway network, found that flows by dif- ferent commodities were fairly similar both seasonally within a year and temporally within a day. This seasonal finding was compared with economic trade data from the economic census of manufacturers. The comparison showed that economic activity by commodity/industry, which would be expected to result in freight flows, was also generally uniform throughout the year. ⢠Research in the use of publicly available commodity flow data found it to be suitable for use as an RP survey to develop mode-choice parameters. Sufficient data were available from a variety of sources that could provide information about possible decision variables affecting mode choice. The analysis showed that distance was the primary determinant of mode choice for most commodities, and that other deci- sion variables were only significant when used in a function together with distance. The inability to develop better mod- els of freight mode choice suggests that those modal deci- sions are due to localized logistics and business decisions that might not be easy to forecast. The inability to define bet- ter mode-choice functions suggests that methods that pivot from observed mode shares might be more appropriate. The literature review, survey, and research led to the devel- opment of a proposed guidebook for freight forecasting. The proposed 10-step process should provide suitable guidance for transportation planners to include freight flows, and flows of commercial trucks serving purposes other than carrying freight, into their forecasting process. Section 3.2 of this report discusses topics that, although not chosen for additional research in this project, were identified as areas that might fill critical gaps in the freight forecasting processes. Additionally, the research topics that were addressed suggested the following additional avenues for research: ⢠The GPS research topic suggests that the utilization of commercial subscription GPS data, especially as these data are improved through the addition of more explanatory variables such as engine status or vehicle type, is especially promising. ⢠The seasonal and temporal flow research topic suggests that additional emphasis on obtaining complete continuous truck classification count data for entire years, and the uti- lization of that data to develop suitable factors, is warranted. ⢠The research in the use of commodity flow databases as an RP survey topic suggests that the utilization of flow data for historical years, as well as potential decision variables for these same years, could lead to promising insights about how mode-choice decisions are made. C H A P T E R 5 Conclusions and Recommendations
