After growing steadily for several decades, passenger vehicle miles traveled (VMT) in the United States unexpectedly leveled off in the 2000s. The growth rate of VMT has since rebounded, and determining the factors that explain these developments has implications for future US oil consumption and greenhouse gas emissions. We show that changes in the demographic and economic characteristics of households in the United States, rather than changes in driving habits, explain most of the recent dynamics. These results suggest that over the next decade, VMT in the United States will continue to grow roughly at historical rates, causing substantially higher oil consumption and greenhouse gas emissions than if persistent changes in household driving habits explained the recent changes in VMT.

Air quality has been an issue of growing importance to the transportation sector since the enactment of the Clean Air Act Amendments of 1990 and the Transportation Equity Act for the 21st Century in 1998. According to these acts, states and local governments are required to attain and maintain National Ambient Air Quality Standards. The MOBILE model is the mobile emission factor model used in estimating air pollutants generated by mobile sources. In order to obtain accurate emission estimates, MOBILE must be provided with sound input data that accurately reflect local conditions. Among many input factors, vehicle miles traveled (VMT) fractions - the percentage of VMT for each vehicle type by roadway functional class - play a critical role. In this study a new methodology for estimating locally specific VMT fractions as an input to the MOBILE model was developed. Based on this methodology, VMT fractions were computed for the six non-attainment areas in Virginia: Frederick County, Fredericksburg, Hampton Roads, Northern Virginia, Richmond, and Roanoke. These estimates were compared with fractions estimated using existing methodologies. The comparison revealed significant differences. These differences, coupled with the fact that the proposed methodology uses significantly more local data and requires fewer assumptions than existing methods, illustrate the need for the Virginia Department of Transportation (VDOT) to reconsider its approach to applying the MOBILE model. Based on the results of this research effort, it is recommended that VDOT's Environmental Division use the proposed VMT fraction estimation methodology to generate input to the MOBILE model for mobile source emission estimates. This methodology will benefit VDOT by estimating mobile source emissions that better reflect local conditions. The cost of implementing the recommendation is minimal. Estimation of VMT fractions is a current activity, and the new methodology requires equivalent or less effort to the existing approach. In addition, required data for the proposed methodology can be obtained at no additional cost.

Due to California State mandates to reduce greenhouse gas (GHG) emissions related to automobile use, Vehicle Miles Traveled (VMT) has become an important indicator of driving activity in a jurisdiction and subsequent GHGs generated by it. The regional organizations tasked with the implementation of public policy designed to reduce GHG emissions by automobiles are California's Councils of Governments (COGs) and Metropolitan Planning Organizations (MPOs). The purpose of this thesis is an examination of whether specific policy activities undertaken by these organizations have had any effect at reducing VMT. A few examples of these policy activities include transit-oriented development and Blueprint strategies that include limiting urban sprawl and managing regional growth. To accomplish this, I utilized both a quantitative regression analysis of data gathered quantitative data from multiple sources including the California Department of Transportation, United States (US) Census Bureau, Center for Health Statistics, and California Association of Councils of Government. For my dependent variable, I chose total VMT because it measures driving activity. My key explanatory variables are Single-County COG, Multi-County COG, and Blueprint. My results show that both of the COG variables have a negative impact on VMT totals, but the Blueprint variable has a positive effect on VMT. More specifically, the Multi-County COG has greater effects on VMT reduction than Single-County COGs. This suggests that regional cooperation is helpful in reducing VMT. Furthermore, I collected qualitative data by interviewing two representatives each from two different COGs. I asked them if they would consider a COG/MPO an effective organization to reduce VMT, to which they both agreed it is. I also asked if they thought the VMT mandated totals would be achieved by the proscribed due dates, and both thought it was not possible. The results provided in this study, unfortunately, are not conclusive in regards to the effectiveness of COG and MPO policies to reduce VMT. The purpose of including a Blueprint variable was to account for regional policies, and since that variable showed a positive correlation to VMT totals, I am not certain those policies are effective. However, I believe that my study is insightful and provides a starting point for tracking potential causes for changes in VMT.

Vehicle Miles Traveled (VMT) is a critical measure of highway system performance used extensively in highway transportation management not only for reporting to oversight agencies such as the FHWA but also as an input for financial analysis, resource allocation, and impact assessments. In the current era as highway revenue from fuel taxes continues to fall and direct user charging such as VMT fees become increasingly attractive, consistent and reliable VMT estimates have become critical for evaluating highway funding options. In the current practice at most highway agencies including the Indiana DOT, there exists several alternative methods for VMT estimation that typically yield a spectrum of estimates that are inconsistent and for certain methods, even inaccurate. This study was commissioned by the Indiana Department of Transportation (INDOT) to develop a benchmark method for VMT estimation and to provide calibration factors for adjusting the VMT estimates derived from the other VMT estimation methods. The benchmark method used in this study was a segment-level framework that decomposes the entire road inventory into links and for each link, determining the product of the traffic volume and the inventory length. For the state highway system, the entire population was used; a comprehensive database was developed which facilitates extensive aggregations of VMT by geographical scope, route, functional class, and vehicle class. For the local roads, a sample of counties of different spatial locations and degrees of urbanization were used, and cluster analysis, geographic information systems (GIS), and spatial interpolation techniques were used to expand the VMT estimates from the local road samples to the population of all counties in the state. The results of this study indicate that there is significant variation, with respect to the benchmark method, of the VMT estimates of the other estimation methods. An implementation platform was developed in this study to produce outcomes that address the VMT data needs of the intended end users and stakeholders; this can be expanded to include new roads in future. It was determined that the current statewide VMT (2013) is 78 billion vehicle-miles, which is expected to grow to 95 billion vehicle miles in 2035.

The vast majority of the U.S. population - some 80 percent - now lives in metropolitan areas, but population and employment continue to decentralize within regions, and density levels continue to decline at the urban fringe. Suburbanization is a long-standing trend that reflects the preference of many Americans for living in detached single-family homes, made possible largely through the mobility provided by the automobile and an extensive highway network. Yet these dispersed, automobile-dependent development patterns have come at a cost, consuming vast quantities of undeveloped land; increasing the nations dependence on petroleum, particularly foreign imports; and increasing greenhouse gas (GHG) emissions that contribute to global warming. The primary purpose of this study is to examine the relationship between land development patterns, often referred to as the built environment, and motor vehicle travel in the United States and to assess whether petroleum use, and by extension GHG emissions, could be reduced through changes in the design of development patterns. A key question of interest is the extent to which developing more compactly would reduce vehicle miles traveled (VMT) and make alternative modes of travel (e.g., transit, walking) more feasible. The study is focused on metropolitan areas and on personal travel, the primary vectors through which policy changes designed to encourage more compact development should have the greatest effect.

This report 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.