Transportation planners have relied heavily on the decennial Census "long form" data because it provides detailed demographic characteristics along with journey-to-work data for small units of geography such as census tracts or traffic analysis zones (TAZs). It is the long form that provides data for the Census Transportation Planning Package (CTPP), the mostly widely used database for transportation planning. Nevertheless, the 2000 Census was probably the last time that the long form will be included in the decennial Census because of Congressional concerns about privacy and the burden on the American public.
The U.S. Census Bureau plans to replace the long form with a continuous data collection program called the American Community Survey (ACS). The transportation planning community needs to know how to use this new source of data in applications such as long-range planning and forecasting, environmental and project analysis, and descriptive statistics. The ACS differs from the decennial Census in many ways, especially as it represents a change from data collected at a single point-in-time (April 1, 2000) to data collected continuously throughout the year and summarized annually for large geographic units. Data for TAZs or tracts will be available based on a moving average of data accumulated over a 5-year period.
The ACS provides new opportunities and challenges for assessing transportation trends. Guidance is needed on the application, interpretation, and presentation of these new data for transportation planning practitioners and policymakers.
The objective of this research is to develop a practitioner guidebook for incorporating ACS data into the transportation planning processes at national, state, metropolitan, and local levels. The guidebook must evaluate ACS data and products and demonstrate their uses within a wide range of transportation planning applications. Recommended applications and procedures will be based on both theoretical and practical considerations.
Accomplishment of the project objective will require at least the following tasks.
Based on interactions with state and local officials and consideration of extant literature and research in progress, critically review current and potential use of census-related data in transportation planning. This review will identify critical areas in the transportation planning process that are dependent on census data and affected by elimination of the long form. Emerging statistical methods that can accommodate continuous measurement and the particular needs of transportation in the treatment of small sample size observations provided over time should be emphasized. A list of critical issue areas will be developed and submitted to the panel for review. (2.
Compare the outputs from the new ACS with those from the decennial Census long form. Describe advantages and limitations for transportation planning applications at differing geographies and timeframes. These applications may include, but are not limited to, travel-demand forecasting, project planning, and analysis of socioeconomic trends. Describe the impacts of the ACS on the use of residence-based summary characteristics data. (Workplace-based and home-to-work flow data will be provided to the contractor for use in Phase II.) Using available ACS data, representing different geographic areas and population sizes, evaluate relevant population and household characteristics. Geographic comparisons will be made for counties, places (incorporated or unincorporated areas greater than 65,000 population), and census tracts. Some of the data-quality issues that should be addressed include seasonality; moving averages from accumulations over time; and differences in response rates, sample rates, sample weighting, and imputation. Standard errors based on the different surveys (decennial Census long form and ACS) will be evaluated for related variables and the geographic units listed above. (3
.) Prepare a detailed outline of the guidebook, recognizing issues relevant to transportation planning, such as:
Description of the ACS and its capabilities, strengths, and weaknesses;
Trend analysis tools;
General socioeconomic and transportation-related characteristics;
Annual and multi-year data summaries;
Residence- and work-based analyses;
Response to emerging transportation planning capabilities;
Statistical techniques and methods;
Case studies of ACS site data; and
Complementary surveys for cross-checking with ACS.
(4.) Submit an interim report that documents the work performed in Tasks 1 through 3 and recommends any needed revisions to the work plan for the remaining tasks. Discuss this information at a meeting with the panel and gain NCHRP approval before proceeding with Phase II.
PHASE II (5.) In order to test the effects of the ACS for workplace-based and home-to-work flow analyses, a test data set will be developed and provided to the contractor by the U.S. DOT, tabulating the 1999-2001 ACS test sites. These tabulations will include residence, workplace, and home-to-work flow data at different geographic levels including tracts and TAZs. Evaluate these data to determine differences between ACS and decennial census data products and their impacts on transportation planning. (6.) Recommend new transportation data products based on the ACS data, incorporating single-year and multi-year summaries. Suggest approaches for integrating workplace and home-to-work flows, including the use of microdata and tract and TAZ aggregations. (7.) Prepare a draft guidebook and related presentation materials (such as PowerPoint presentations and summaries) for review by the panel. Obtain comments and suggestions before preparing final products. (8.) Based on the results of the preceding tasks, develop and submit to NCHRP, the guidebook and final research report. Identify research and training needs emanating from this project.
This task was completed and the final report is available in hardcopy and electronic format (http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_588.pdf)