The Case for Moderate Growth in Vehicle Miles of Travel: A Critical Juncture in U.S. Travel Behavior Trends

This paper hypothesizes that the United States has reached a critical juncture in terms of national mobility trends and underlying socio-demographic conditions and travel behavior that will result in more moderate rates of annual vehicle miles of travel (VMT) growth in the future. However, slower VMT growth may not portend lower rates of congestion growth. Travel is acknowledged to be an integral part of the quality of life and, consequently, travel behavior is complex and related to a host of social-economic characteristics of the traveler and the transportation system. This paper outlines the major factors that influence travel behavior. The direct factors are discussed first using primarily empirical data. That is followed by a discussion of the indirect or underlying factors. These are divided into three major categories: socio-economic conditions, transportation system conditions, and land use conditions. This paper will concentrate most specifically on the role of the socio-economic conditions and travel behavior. These factors include: population age profile, auto availability, licensure rates, household size, shared ride propensity, transit use propensity, walk propensity, male and female labor force participation, real income per capita, and land use patterns. Several of these factors appear to be undergoing historic trend reversals. In addition, new evidence suggests that congestion levels have reached the point where average travel speeds are declining. This declining speed may provide additional dampening of VMT growth if travelers remain within a relatively stable travel time budget. While this paper builds a case for slowing VMT growth nationally, it hypothesizes that there may continue to be declining system performance (speed) in spite of slower VMT growth due to the fact that more of the roadway system is at or near critical congestion points and hence more susceptible to performance deterioration with modest increases in travel demand. It also suggests that the land use pattern impacts on travel behavior and person travel time budget growth are the least well understood factors and the possible weak links in reaching conclusions about the ultimate course of VMT growth. Two forecasts of future VMT levels are provided that build on the data and information presented in the body of the paper.


  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Figures; References; Tables;
  • Pagination: 49p

Subject/Index Terms

Filing Info

  • Accession Number: 00986363
  • Record Type: Publication
  • Created Date: Feb 15 2005 12:00AM