Updating Procedures to Estimate and Forecast Vehicle-Miles Traveled

Procedures developed for the estimation of Vehicle-Miles of Travel (VMT) have been fraught with problems of inaccuracy. Emphasis on environmental issues (air quality), as mandated by current regulations (CAAA, ISTEA-91, and TEA 21), requires State DOTs to accurately estimate travel on their highway infrastructure. The Federal Highway Administration (FHWA) has developed, and subsequently modified, the Highway Performance Monitoring System (HPMS) to assist in data collection and reporting. INDOT currently estimates VMT by a method that closely follows the HPMS method. Roads that are not on the state highway system (minor collectors, urban collectors and local) are not represented in the estimation procedure, thus INDOT is uncomfortable with the accuracy of the statewide VMT estimates reported to the FHWA. Cross-classification models are being developed, based on licensed driver and household travel characteristics, with data from the Nationwide Personal Transportation Survey (NPTS). These models are intended to address the problems of sampling bias associated with current VMT estimation procedures because they are independent of highway functional class. Variables adopted in these models include average annual miles driven per licensed driver, by sex and age cohort, and average annual household VMT based on selected demographic and socioeconomic characteristics.