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16 CHAPTER 5 Data Sources In order to forecast statewide freight flows, data are When conducting a survey of freight movements, one needed to develop and validate the models and methods encounters a basic problem: determining the size of the mar- used as inputs. Quality and precision are the keys to freight ket that should be surveyed. Conducting a cordon survey modeling, with the accuracy of the freight flow forecast around an entire state boundary is generally impractical, and dependent on the accuracy of the database. If the underlying matching vehicles passing through a statewide cordon can be database is not complete and correct, then the estimated extremely difficult. Cordon surveys do not usually provide freight flow will be inaccurate. This section of the Toolkit information about the contents of vehicles, such as, com- identifies data sources unique to freight forecasting or modity information, which makes it impossible to tie the applied to freight forecasting in a unique way. General data freight flows back to economic development data. sources used in transportation forecasting should be famil- Generally, shipper and carrier surveys prove more man- iar to users of the Toolkit and will be mentioned briefly. ageable. In a shipper survey, a major shipper is asked to fill Freight-specific data sources for important databases also out a form detailing each shipment dispatched in a given time will be briefly summarized, while sources used in the case period. The information collected might include the type of studies will be described in more detail. commodity, the place of origin, the destination, the transport mode or modes, the dollar value and physical volume of the shipment, and other general information. In a carrier survey, 5.1 Model Development a major carrier is asked to detail all the shipments carried and As described in Sections 4.0 and 6.0, statewide freight fore- possibly also the route chosen. With the consent of the car- casting methods employ a variety of techniques, models, and rier's management and staff, electronic driver information formulas for processing data. The nature and form of the systems may be used to collect similar data. Determining a equations and the values for their coefficients and parameters statistically valid sample of shippers and carriers for a specific are determined through a model development process famil- statewide survey and the appropriate expansion factors is iar to those that have developed passenger forecasting models. extremely difficult and expensive. However a shipper diary The sources of this data for freight are described below. survey is regularly conducted by the U.S. Census Bureau for the CFS. Local Surveys Compilations The construction of a passenger transportation forecasting model often begins with a travel survey. A travel survey gath- Developers of freight forecasting models may wish to avoid ers information about the number of trips, the purpose of the expense of conducting a behavioral survey and instead use these trips, the time the trips were taken, the cost, the distance the rates, coefficients, and relationships developed by others. traveled, the mode choice, and information about the trav- While not as well developed as those for passenger planning, eler. A travel survey thus provides the behavioral data needed several publications provide values that can be used in truck to establish the trip generation, trip distribution, mode split, generation and distribution models. These publications and assignment relationships specific to a study area. The include the Institute of Transportation Engineers' Trip survey size must be designed to provide a statistically valid Generation Handbook7, the National Cooperative Highway sample of all potential travelers. Research Program's Truck Trip Generation Data8, and the
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17 Federal Highway Administration's Quick Response Freight providing a more modern focus and a better link to industry Manual3, and Accounting for Commercial Vehicles in Urban classification and output measures. Transportation Models.9 Due to variations in methodology, sample size, and other changes, the CFS is not particularly consistent from year to year, making it hard to build time-series data. Nonetheless, National Surveys the CFS remains the only shipper survey to which a response Shipper surveys typically require a nationwide sample. is mandatory. As such, it is less likely to be biased than other While a survey of shippers within the target market area will shipper surveys. provide a sound picture of outbound shipments, this limited In terms of statewide forecasting, the CFS presents diffi- coverage will otherwise miss inbound activity. To avoid the culties. Since the survey is predominantly designed to map size and complexity of conducting such a study for an indi- national-level traffic, the small sample size within each state vidual freight forecasting project, existing surveys may be means that data must be aggregated to preserve shipper con- obtained. The two most common surveys, the CFS and fidentiality. Consequently, origin and destination data are TRANSEARCH, are described in detail as part of this Toolkit. publicly released on CD-ROM at two aggregation levels: Also described is the FAF's Commodity Database, a publicly state-to-state and between 86 of the largest metropolitan available database created from TRANSEARCH. areas (portions within the primary state boundary only). Fur- thermore, the 1997 data are available only as predefined data files through a browser, as shown in Figure 5.1. While com- Commodity Flow Survey modity, origin, destination, and mode information is avail- CFS is conducted every five years as part of the U.S. Cen- able, only three of the four characteristics are reported in any sus Bureau's Economic Census and is designed to provide one table. Individual tables by origin, destination, and com- data on the flow of goods and materials by commodity, ori- modity must be transformed and aggregated to produce a gin, destination, and mode of transport. Prior to 1997 the national database. Additional processing is necessary to esti- CFS reported commodity information using the STCC code. mate data that is aggregated or suppressed to preserve confi- Beginning with the 1997 CFS, the SCTG codes were used, dentiality. Figure 5.1. Commodity flow survey.
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18 The 2002 data has been collected and partial releases began TRANSEARCH's county-to-county market detail is devel- to be made available in 2004. The 2002 survey excluded ship- oped through the use of Reebie Associates' Motor Carrier ments by establishments classified in the North American Data Exchange inputs and its Freight Locator database of Industry Classification System (NAICS) as farms, forestry, fish- shipping establishments, which provides information about ing, government agencies, construction, transportation, and the specific location of manufacturing facilities, measures of most retail and service industries. The 2002 survey also facility size (both in terms of employment and annual sales), excluded shipments from logging establishments, because and a description of the products produced. under NAICS the classification of this industry moved from Primary coverage of truck traffic is limited for nonman- manufacturing (included in the scope of the CFS) to agriculture ufactured products. For manufactured products informa- (out-of-scope for the CFS). The CFS is a survey of domestic tion is provided using the STCC Code, which can be establishments and measures shipments leaving an establish- aggregated from a four-digit level. Supplemental material ment's facility, and it includes exports but not imports (unless for agricultural and mining resource extraction shipments the imported goods are received by an included domestic busi- from the source to a processing plant not ordinarily cov- ness at the port of entry and reshipped by that business). The ered in commodity flow surveys is available for an addi- 2002 CFS also excludes shipments of crude petroleum by the oil tional charge. and gas extraction industries because of issues with how these Traffic movements originating in warehouses or distribu- companies record and report shipment information. tion centers or drayage movements of intermodal rail or air The 1997 CFS is available on CD-ROM from the U.S. freight are shown as STCC 50. These are by definition truck Census Bureau at http://www.census.gov/econ/www/cfsmain. movements. Movements to warehousing and distribution html. The 2002 CFS will be available in February 2005. centers may be by other STCC codes and by any mode. Details on the types of items being moved in STCC 50 are not available. TRANSEARCH The CFS defines the use of multiple modes, such as truck TRANSEARCH is a database of freight traffic flows avail- and rail, as a separate mode. The TRANSEARCH database, able from Reebie Associates. Although proprietary, it also is shown in Figure 5.2, is an unlinked trip table that reports the the most commonly used source of freight data; four of the portion of a trip by each mode, and in some cases submodes, case studies reported in this Toolkit rely on TRANSEARCH. separately. This allows the volume of shipments at inter- TRANSEARCH uses several mode-specific data sources to modal transfer points to be identified, but the information on create a picture of the nation's freight traffic flows on an ori- the lining of the trips is lost. gin to destination commodity basis, refining the geographic As discussed, TRANSEARCH is constructed from many market identification to the county level. commercial and public sources of data, representing domes- TRANSEARCH is updated annually using the following tic and NAFTA trade flows. Economic modeling is used to sources: adjust the surveys where data is lacking or confidential and to check elements such as spatial patterns and logic. Given the 1. Annual Survey of Manufacturers by state and industry; complexity of its sources and the additional analysis that is 2. Surface Transportation Board (STB) Carload Rail Waybill undertaken, the construction of TRANSEARCH cannot be Sample of market-to-market rail activity by industry; easily summarized. This inability to completely document all 3. Army Corps of Engineers waterborne commerce data elements and proprietary sources has led to some concerns by describing market-to-market water activity by industry; some users about the data's inclusiveness. Despite these con- 4. Federal Aviation Administration (FAA) enplanement sta- cerns, TRANSEARCH is an accepted freight database widely tistics and airport-to-airport cargo volumes; used for planning by the FHWA, many U.S. states and met- 5. Rail, water, and air freight flow data deducted from the ropolitan planning organizations (MPOs), as well as private Bureau of Census Annual Survey of Manufacturers (ASM)- freight carriers and shippers. based production data; and The inland or surface movement of import and export 6. Reebie Associates' proprietary Motor Carrier Data Ex- traffic volumes to locations outside of North America is change Program, which provides information on actual included in the data but only to and from the location market-to-market trucking industry movement activity. where the freight crosses the U.S. border. However, the The truckload sample covers about 6% of the market, and flow patterns of this freight are based on the movement Reebie Associates' less-than-truckload sample is about patterns of domestically sourced goods in the same market 40%. In total, information is received on over 75 million areas and are not the actual movements of the import/ individual truck shipments. export freight.
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19 Figure 5.2. TRANSEARCH database. TRANSEARCH is available for purchase from Reebie Analysis (BEA) region to BEA region level at the five-digit Associates at http://www.reebie.com. Standard Transportation Commodity Code level. The STB Waybill Sample is a stratified sample of carload waybills for STB Carload Rail Waybill Sample terminated shipments by railroad carriers. STB is the official authority of the Carload Waybill Sample. Army Corps of Engineers Waterborne Railroads terminating over 4,500 cars per year are required to Commerce Data file a sample of waybills with the STB. The primary purpose of the Carload Waybill Sample is regulatory oversight. The Waterborne traffic movements are reported to the Army Waybill Sample contains rail shipments data such as origin Corps of Engineers by all vessel operators. The reports are gen- and destination points; type of commodity; number of cars, erally submitted on the basis of individual vessel movements tons, revenue; length of haul; participating railroads; inter- completed. For movements with cargo, the point of loading change locations; and Uniform Rail Costing System shipment and the point of unloading of each individual commodity variable cost estimates. It contains confidential information must be delineated. Military cargo moved in commercial ves- and is used primarily by Federal and state agencies. While the sels is reported as ordinary commercial cargo; military cargo Waybill Sample is not available for public use, a public-use moved in Department of Defense vessels is not reported. In version contains aggregated nonconfidential data. Move- summarizing the domestic commerce certain movements ments are generally aggregated to the Bureau of Economic Cargo carried on general ferries; coal and petroleum products