Survey (ACS) are critical data elements that support the analysis of transportation plans, policies, programs and project selection. Changes in the data products over the last 10 years and ongoing staff turnover have left a void of expertise in effectively using this data to support transportation planning. Additionally, there is no centralized resource location where one can go to learn how to use the data for real world applications. This results in wasted time and questionable analysis.

When the ACS was introduced by the Census Bureau as the replacement to the Long Form it brought with it a change in how the data was collected and packaged for public release. This in turn, brought a whole new set of data issues for the transportation analyst to understand and cope with.  Margins of error, privacy protection rules and procedures, imputation, rounding, data suppression, changes to the survey instrument and variables, and period estimates all have stretched the learning curve for the user. Staff from the states, MPOs and transit operators all have struggled with the use and application of the ACS and data products derived from it like the CTPP and Public Use Microdata Sample/Public Use Microdata Area (PUMS/PUMA).

Under NCHRP Project 08-123, “Census Data Field Guide for Transportation Applications,” Cambridge Systematics was asked to develop a field guide for the transportation community on how to best use Census data, including the ACS, CTPP, LODES Employment-Household Dynamics (LEHD), and PUMS/PUMA, to address transportation issues. To support the use of the field guide, the research team developed tools for transportation analysts.

In addition to the field guide that published as NCHRP Research Report 1108, a number of deliverables are available on the TRB website at trb.org by searching for NCHRP Research Report 1108. The deliverables are as follows:

• Case Studies Notebook
• Travel Survey Weighting Spreadsheet