The purpose of the project was to develop estimates of average weekday household person trips, vehicle trips, person miles traveled, and vehicle miles traveled, for all census tracts in the United States. The estimates were made using national travel data collected in the 2009 National Household Travel Survey (NHTS), sponsored by the Federal Highway Administration, and applied to individual census tracts using the 2005 to 2009 American Community Survey (ACS) estimates from the Bureau of Census.
The NHTS national sample was divided up into six regions, and within each region further divided up into urban, suburban and rural areas. This was done to reduce geographical differences and improve the accuracy and reliability of the estimates. Several demographic and household characteristics were used to estimate the travel variables within each category, using a series of regression equations. These characteristics include average household income, number of household vehicles, number of household members, number of workers in the household, if the house is owned or rented, if the household incudes one or more children, and a combination of one versus multiple member households and households with one or more persons 65 or more years old.
The estimated regression equations were then applied or transferred to individual census tracts using the household characteristics for those census tracts using the Census ACS data. A SAS database has been created with those estimates, along with a data dictionary, that can be accessed at the National Household Travel Survey homepage.
A small number of census tracts do not contain estimates for a variety of reasons, such as census tracts with zero population, or census tracts with very unusual demographic or travel characteristics.