Planopedia

While "vehicle miles traveled" might sound like a self-explanatory term, the application of this seemingly simple concept has powerful implications for transportation planning and policy. 

The U.S. Department of Transportation defines vehicle miles traveled (VMT) as "the total annual miles of vehicle travel divided by the total population in a state or in an urbanized area." The DOT notes that federal data has some limitations, using only 4,000 automatic traffic recorders across the country, and those only on major roads. Nevertheless, the metric is used, along with travel times and costs, to measure vehicle travel demand and make policy decisions regarding roadways and other transportation infrastructure. The Federal Highway Administration reports VMT data on a monthly basis.

With the federal Highway Trust Fund facing a persistent deficit from inflation and increasing numbers of electric vehicles on the road, some experts recommend replacing the gas tax with a VMT tax to supplement the road funding that has traditionally come from gas tax revenue. According to this argument, using VMT would prevent electric vehicle drivers from avoiding their contribution to road funding and maintain a robust road projects fund as the EV market share grows. Internationally, countries such as Germany, Belgium, and Poland have a VMT tax on large trucks, while New Zealand applies a VMT tax to all heavy and diesel-powered vehicles. In the U.S., Oregon's OReGO program allows drivers to essentially choose between paying the state's 38-cents-per-gallon fuel tax or enroll in the program, which lets them opt to pay a VMT tax and receive a fuel tax credit instead. Utah began its own VMT tax pilot program for electric vehicles in January 2020, giving users the option to pay either a 1.5-cent-per-mile or annual $120 (for EVs) or $20 (for hybrids) fee.

VMT is also becoming a popular metric for evaluating the impact of housing projects and other developments. Under some state and local environmental impact regulations, developers must submit an assessment of the projected impacts of their projects on transportation. In the past, transportation impacts were largely measured using level of service (LOS), which prioritizes traffic throughput and travel speed. In 2020, California changed this approach, shifting to VMT as a more appropriate way to focus on emissions reductions and encourage land use decisions that don't induce more sprawl. Rather than assessing the capacity of roadways to accommodate traffic, a VMT-centered policy seeks to reduce greenhouse gas emissions and improve air quality, which the state, in making its decision, argued is a more accurate assessment of a project's true transportation impacts. California's new rules ask developers to project VMT created by their projects and, if they reach a certain level, provide for mitigations by taking steps that can include: improving access to transit and local amenities, incorporating affordable housing, and/or providing incentives to increase transit use.

Proponents of VMT as a metric argue that it provides a more holistic measure than LOS of how a project will affect congestion, greenhouse gas emissions, and air quality. Reducing VMT is associated with reductions in carbon emissions and congestion, leading to improved air quality and decreased commute times. Hence, VMT can serve as one metric for assessing the success of policies designed to fight climate change, improve public health, and encourage the use of public transit and other sustainable transportation modes.