concerns to raise with the Census Bureau about the data products. Their efforts in this regard go back to the beginning of the ACS (see, for example, Bureau of Transportation Statistics, 1996). With funding from federal transportation agencies, a committee of the National Research Council’s Transportation Research Board organized a conference on “Census Data for Transportation Planning—Preparing for the Future” in May 2005. The conference covered a wide range of topics and issues regarding the opportunities and challenges presented by the advent of the ACS (see http://trb.org/conferences/censusdata/Program.pdf).
The transportation community’s interest in the ACS is explained by the central role that the long-form-sample data have historically played in transportation applications ranging from nationwide program planning and evaluation to local analysis of commuting patterns. Questions on place of work, means of transportation to work, length of commute, and vehicle ownership have been included on the long-form questionnaire for three or more decades, as have questions about disabilities that make it difficult for people to work or to go outside their homes (see Citro, 2000b).
The U.S. Department of Transportation has worked closely with the Census Bureau and with state transportation departments and metropolitan planning organizations to improve the quality of the data on place of work (by, for example, encouraging large employers to inform workers of the addresses to report for particular workplaces) and to develop special tabulations for transportation users. The Census Transportation Planning Package (CTPP) has been produced from censuses beginning in 1970 and includes tabulations of households and workers by place of residence, workers by place of work, and flows between place of residence and place of work for each traffic analysis zone (TAZ). There are a large number of such zones, designated by states and regional transportation agencies, each comprised of one or more blocks, block groups, or census tracts within metropolitan areas.13
Regional and metropolitan transportation planning organizations are also heavy users of the long-form-sample PUMS 5 percent sample files, which in 2000 provided records for 14 million individuals, with geographic identification by state and PUMA (areas of about 100,000 population). The long-form-sample PUMS files are the basis of sophisticated transportation activity modeling systems that contain synthetic population models for a base year and, say, 20 years into the future. The population models are calibrated to control totals for the base year and future years on total households, households by income level, and other characteristics that are estimated by the regional organization at the county or TAZ level. The models are then used to predict activity and travel patterns at the person, household, or trip level.
See http://www.trbcensus.com/ctpp.html; National Research Council (1995:App. G).