Exploring the Use of VMT as an Evaluation Metric Within Virginia’s Transportation Planning Process 

About the report

For several decades, transportation planners and engineers have used automobile Level of Service (LOS) to communicate transportation system conditions. In Virginia, stakeholders such as Fairfax County officials have shown interest in supplementing LOS with vehicle miles traveled (VMT), which can be a useful measure of vehicle travel and a proxy for other categories like vehicle emissions. Although using VMT to describe overall travel patterns is not new, some states and localities have adjusted their transportation analysis processes in recent years to focus on VMT in conjunction with VMT reduction goals. In a LOS-focused process, traffic congestion often drives mitigation strategies. In a VMT-focused process, the overall goal of reducing the negative effects of added local or regional vehicle travel from land development and transportation projects drives mitigation strategies.

The purpose of this study was to explore how VMT might be used as a transportation evaluation metric in Virginia, based on reviewing how VMT has been applied elsewhere and translating such uses to the Virginia context, by (1) documenting LOS and VMT use in Virginia, (2) assessing how other states use VMT, (3) interviewing planners in California and Oregon, and (4) evaluating two Virginia pilot projects.

Findings indicate that VMT is currently used in congestion management to understand induced demand, in environmental analysis to estimate mobile source air toxins and greenhouse gases, in safety evaluations as a measure of exposure, and in efforts to further equity and economic development. The drawbacks and complications of using VMT as a metric include difficulties collecting data or extrapolating VMT from travel demand models, the need for nuance when using VMT as a proxy measure for smart growth or environmental health, and the implementation difficulties that often attend novel applications. Two findings are noteworthy: (1) VMT is used at several points in Virginia’s planning process—more than was expected at the outset of this study—which may surprise some localities because they often focus on one particular planning element (land development), which uses LOS—thus, this topic could be a subject for greater Virginia Department of Transportation and locality collaboration—and (2) induced VMT calculators exist, but the geographical extent of the analysis greatly affects the interpretation—for example, whether to consider VMT on just a reconstructed segment or a certain distance away from the site—so choosing the right extent for such calculations would be an important implementation consideration. This report recommends that the Virginia Department of Transportation consider the pros and cons of using VMT when updating relevant guidance documents.

_{Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.}

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