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33 CHAPTER THREE CASE STUDIES This chapter presents five case studies of statewide models. except that there are three additional trip purposes to account The case studies emphasize the differences between statewide for long distance travel. and urban models. Two case studies, Kentucky and Indiana, focus on the passenger component and two other case studies, The KYSTM highway network is very large, spanning all Virginia and Wisconsin, focus on the freight component. The of the contiguous 48 states. The network, as shown in Figure fifth case study, Ohio, presents a comprehensive framework 6, is focused on the state, with considerable detail extending for dealing with both passenger travel and freight while ac- approximately halfway into its neighboring states. This net- counting for changing locations of economic activity. These work has more than 77,000 links, more than 3,600 zones particular case study states were selected because their mod- within the state, and more than 1,100 zones outside the state. els integrate a number of features described in chapter two, Figures 7 and 8 illustrate the Kentucky zone system. The ex- and they do not duplicate material found in the report from pansive nature of the network has allowed analysis of diver- NCHRP Project 8-43. sion from out-of-state highways. CASE STUDY 1: KENTUCKY PASSENGER Kentucky Statewide Passenger Component Summary COMPONENT State population: 4.1 million State area: 40,411 square miles Kentucky has had one of the longest involvements with Gross state product: $129 billion statewide travel forecasting, starting in 1971. The Kentucky No. of internal zones: 3,644 statewide model (KYSTM) has just recently been updated External zone structure: Halo + BEA regions (a previous version was summarized in the Guidebook). Internal zone structure: TAZs, aggregations of TAZs Kentucky's model has always had a goal of being efficient No. of external zones: 1,109 in its expenditure of resources, achieving a very useful No. of links: 77,272 model on a small budget by piggybacking on data obtained Passenger modes: Automobile from existing sources. The only data collection specifically Trip purposes: for the model was the purchase of additional NHTS samples. Home-based work The model also has a truck component. Kentucky's model Home-based nonwork is presented here as an example for states with modest fore- Nonhome-based casting needs and states now considering models for the first Long distance business time or that are in the process of reactivating a dormant Long distance--Recreation/vacation model. Long distance--Other Special generators: Military bases The model is well integrated with agency decision making. Trip productions: Rates per household based on MSA size, "The main purposes of this model are to support highway plan- area type ning and investment decisions, to permit a consistent method- Trip attractions: Rates per level of activity ology in project evaluations, and to allow testing alternative Trip distribution: Gravity expression, Fratar land use strategies." Previous versions of the model have been Mode split: None used for corridor planning, project-level traffic forecasts, re- Assignment: Static equilibrium with subzones gional planning and weigh station location. A stakeholder Delay estimation: BPR curves meeting was held early in the process to ensure that the model Major data: NHTS, HPMS, ATS, vendors development met agency needs. The revision took approxi- Time frame: Two years of development time mately 2 years and cost about $370,000. Computation time: 1 h In-house staff: 1 FTE The overall structure of the passenger component consists of three steps: trip generation, trip distribution, and traffic as- The zone structure was built for compatibility with other signment. Only highway vehicles are assigned to a network; databases. It is readily seen that zones well outside of Kentucky therefore, a mode split step is not necessary. The application are based on BEA Economic Areas. Zones within Kentucky of the KYSTM's steps is similar to traditional urban models, were created as part of census TAZ-UP participation. A level
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34 of detail was selected so that the model could evaluate projects such as I-66 and I-69 and still be reasonably accurate within ur- ban areas. Zones were custom aggregated from census TAZs in dense urban areas; however, census TAZs were adopted in fringe urban areas. TAZs in 72 rural counties were built from census block groups or census places. The halo of zones around Kentucky was represented by 660 census tracts and 296 coun- ties. The model was built from secondary data. Data sources included workplace employment data from Woods & Poole, D&B, and Claritas. Trip rate information was derived from the 2001 NHTS. Because there were only 390 samples in the standard NHTS, Kentucky contracted for an additional 1,154 samples to provide better geographic coverage. Household socioeconomic data were mostly derived from the 2000 FIGURE 6 Kentucky's highway network. (Source: Wilbur Smith Census. The census also provided journey-to-work data. Associates 2005a.) Information on long distance travel came from the 1995 ATS. Network data within Kentucky were obtained from the Kentucky Transportation Cabinet Highway Information Sys- tem. Network data outside Kentucky were developed from the NHPN for roadway geography and the HPMS for road- way characteristics. A single trip production rate was applied for any zone for any trip purpose. Trip production rates per household were separately calculated for different MSA sizes and different Claritas area types (rural, town, suburban, second city, and urban), which were included in the NHTS. Trip attraction equations were taken directly from NCHRP Report 187, hav- ing demographic variables of households, retail employees, and nonretail employees. The NHTS also yielded automobile occupancy rates, one for each short distance purpose. The short distance occupancy rates were similar to those seen within urban areas. Long distance automobile occupancy rates were derived from the ATS, as found on Table 4. FIGURE 7 Kentucky's zone system, in state. (Source: Kentucky response to Peer Exchange questionnaire 2004.) Kentucky adopted a philosophy of using actual OD tables wherever possible. Thus, trip distribution was accomplished with a gravity expression only for home-based nonwork and nonhome-based purposes. Friction factors were chosen to match the trip length frequency distributions from the na- tional and Kentucky NHTS. For home-based work, a zone- to-zone production-to-attraction table from the 2000 Census journey-to-work data was Fratar factored. Fratar factored trip tables from the ATS were used for long distance trip pur- poses. Table 5 shows how each long distance trip purpose TABLE 4 LONG DISTANCE AUTOMOBILE OCCUPANCY RATES Long Distance National Kentucky Trip Purpose Sample Sample Business 1.82 1.80 Tourist 3.23 3.31 Other 2.48 2.43 FIGURE 8 Kentucky's zone system, out-of-state. (Source: Kentucky response to synthesis questionnaire February 2005.) Source: 1995 ATS.