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42 CHAPTER 8 Case Studies The model components, class of models, data, and other Objective and Purpose of the Model statewide freight forecasting issues discussed elsewhere in this What need will the forecasting model address? How will Toolkit are not theoretical exercises. They are issues that trans- the model be used? portation planners have confronted and will continue to con- front. So that users of the Toolkit may have the benefit of the experiences of other planners and may see actual applications General Approach of the techniques, 10 case studies have been prepared. Two case studies have been chosen for each of the model classes defined Model class in the Toolkit. The cases studies draw widely from the various Choose from one of the following: model components, and represent a variety of data source applications. To the extent possible, the results of the coeffi- · Flow Factoring; cients, parameters, equations, validation, and other aspects of · O-D Factoring; the case studies have been presented so that users of this Toolkit · Truck Model; can compare their results with the results obtained by others. · Four-Step Commodity Model; and The case studies have been presented using a common · Economic Activity Model. template, presented in Section 8.1. This template not only permits easy comparisons between case studies, but also serves as a useful organizing principle for anyone undertak- Modes ing a statewide freight forecasting project. Answering the What freight modes will the model address? questions in the template helps freight forecasters better un- derstand the specific issues they must face and the choices they can make given the available techniques. Markets This Toolkit is intended to present useful information on a variety of techniques in an accessible format. No single What is the nature of the market that the freight forecast- approach can be considered the correct one, nor does the use ing model must cover (geographic, industries, etc.)? of one approach preclude the possibility of using another in the future. By answering the questions in the template, users Framework should be able to develop an approach that best addresses their specific needs. Will the freight model work within a larger process of preparing transportation forecasts for nonfreight demand, such as passenger travel? If it will be part of a larger process, 8.1 Development of a Forecasting how will the freight model be included? Model Template Background Flow Units Context What flow units will the model be expected to report (an- What is the nature of freight movement in the area for nual tons, daily trucks, daily trucks by truck type, etc.)? Will which the forecast model will be developed? the flow units differ for the individual modal networks?
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43 Data example, from annual to daily flows)? How will these conver- sion factors be obtained? If the conversion factors will be de- Forecasting Data veloped specially for this model, what data source will be used BASE AND FORECAST YEAR SOCIOECONOMIC DATA to develop these conversion factors? What base year data is available to support the model? What geographic units are available? What is the industrial Validation Data breakdown? Is forecast data available, and if so what level of Which of the model components will be validated using geographic and industrial detail is available? Is the forecast data obtained independently of the model development? data developed by a land use/economic model? Is such a What is the source of this data? How will it be used? model to be integrated with the freight transportation model? Model Development EXTERNAL MARKETS Software What data is available for the geographic area outside of the state or primary study area? Is base data available on the What software programs will be used in the development amount of freight that travels to and from these external mar- of this model? What software programs will be used in the kets and the state or other primary study area? Is base data operation of this model? available on the amount of freight that travels between these external markets passing though the state or other primary Commodity Groups/Truck Types study area? What level of geographic and industrial detail is available? Is forecast data available, and if so at what level of Will the freight flow units of the model be distinguished by industrial detail? purpose? For commodity models, what commodity groups will be separately included? Are these aggregations of existing Modal Networks commodity classification schemes? For truck models, what truck types will be separately included? FREIGHT MODAL NETWORKS Are existing travel demand model networks for any of the Trip Generation freight modes to be included in the model? Does sufficient data exist to develop any missing modal networks? Are modal Will a trip generation component be included? If so, how networks that cover any external zones to be included in the will the trip generation rates be developed? For production? model? For attraction? INTERMODAL TERMINAL DATA Trip Distribution Is data available on intermodal terminals where freight Will a trip distribution component be included? If so, will changes modes (ports, airports, and rail terminals, for exam- a gravity model or some other model form be used? How ple) that might be included in the model as special genera- will the model parameters and equations be developed? tors? Does this data include information on the location and capacity of the terminals? Does this data include demand/ Commodity Trip Table usage data for the terminals? If neither a trip generation model nor a trip distribution model will be included, will an existing origin-destination Model Development Data table of freight flows be obtained for inclusion in the model? Will model coefficients and parameters be developed How will this table be updated for forecasts? specifically for this model? If so, what data will be used to develop these parameters and coefficients? Mode Split Will a mode split model be included in the model? Will Conversion Data this component primarily rely on existing mode splits? If so, Will the model need to convert flows from one unit to where will those existing mode splits be obtained? Will the another (for example, from tons to vehicles)? Will the model existing mode splits be modified qualitatively based on need to convert flows from one time unit to another (for expert opinion? Will the existing mode splits be modified