Reducing Vehicle Miles Traveled

What are Policies to Reduce Vehicle Miles Traveled?

Vehicle Miles Traveled, or VMT, is the number of vehicles on the road multiplied by the number of miles they travel.  Transportation greenhouse gas (GHG) emissions are equal to VMT multiplied by the emissions per vehicle-mile.  Thus, there are two ways to reduce transportation emissions: (a) reduce emissions per vehicle by changing vehicles and fuels, and (b) reduce VMT.  This overview describes policy options for reducing VMT.

Person-miles traveled (PMT) is the number of people traveling multiplied by the number of miles they travel. There are two basic options for reducing VMT: (1) reducing travel and (2) keeping PMT constant while reducing VMT.  Shifting from driving alone to ridesharing or traveling by multi-passenger bus can keep PMT constant while reducing VMT.

How Do Policies to Reduce VMT Work?

VMT reduction policies for passenger vehicles incentivize, enable or require travel reduction, ridesharing, or shifting to transportation modes with higher vehicle occupancy. VMT policies can also reduce miles traveled by heavy-duty vehicles and freight transport by improving logistics and optimizing multi-modal transportation options.  These policies can be divided into the following categories:

Reducing the need to travel

  • Land use. The design of the built environment can reduce the need to travel by co-locating where people live, work, learn, access services, and play. “Smart growth” and re-design through land use planning, zoning, development, and housing policies can encourage transportation-efficient communities and regions.
  • Virtual interaction. Incentives to replace physical interaction with virtual interaction through, for example, telecommuting, telehealth, and teleconferencing reduce the need to travel. (Online shopping reduces the need for customers to travel to stores, but it increases the need for package delivery, so it may or may not reduce overall VMT.)

Influencing travel choices

  • Economic incentives and disincentives. Fuel taxes, parking fees, and congestion pricing, for example, may reduce overall travel or shift it to higher-occupancy modes of transportation. Shifting fixed travel costs to variable costs can also affect travel, mode and ridesharing choices.  Owning a vehicle has high fixed costs, so once a vehicle is purchased, vehicle owners will be inclined to use their vehicles rather than other transportation options.  Thus, discouraging individual vehicle ownership (e.g., through higher vehicle registration fees) can encourage travelers to make fairer comparisons between options for individual trips (e.g., between renting a car and taking the bus).  Paying for car insurance per mile instead of per vehicle shifts fixed costs to variable costs, making the incremental cost of a vehicle trip higher and less attractive in comparison to other options.  Ridesharing tax incentives encourage ridesharing, and transit subsidies encourage greater transit use.
  • Requirements and restrictions. Parking restrictions discourage personal vehicle travel, and restricted carpool lanes encourage ridesharing.
  • Providing travelers information about travel options, for example through real-time mobile apps, could enable VMT reductions. For heavy-duty freight, information technologies can improve logistics, reduce “empty” trips, and more.

Key Design Considerations

The overarching design consideration for VMT reduction policies is how one preserves mobility while reducing GHG emissions.  Policies can only discourage travel to the extent the built environment is designed so that people can still get where they need to go.  Policies can only encourage shifting from personal vehicles to other modes of travel to the extent those other modes are available. Policies can only encourage ridesharing to the extent that is a viable option.

Policymakers may also wish to consider how reducing VMT could affect other policies, such as revenues for the Highway Trust Fund through the gas tax.

U.S. Experience with Policies to Reduce VMT

U.S. experience with policies to reduce VMT has been mixed.  U.S. federal transportation policy has mainly focused on enabling personal vehicle travel through investment in roads and bridges, with some investment in transit and smart growth. In most of the United States, the population density is too low to support mass transit, with most metropolitan areas characterized by sprawl.  In 2016, 91% of American households owned one or more vehicles, with about 1.8 vehicles per household. Transit today serves less than 4% of U.S. trips, half of them in NYC. However, many Americans prefer walkable, dense communities and the smart growth and urban re-design policies that support them.  Thus many cities and states have increasingly focused on these policies in recent years.

The recent advent of ride-hailing companies like Uber and Lyft is providing a new mobility option.  Its implications are still unclear.  On the one hand, by substituting for mass transit, it could increase VMT.  On the other hand, ride-hailing could provide first-mile and last-mile service to and from train and bus stations, enabling greater use of transit and blurring the lines between public and private transportation.  Ride hailing could reduce VMT by providing an alternative to car ownership, or it could increase VMT by encouraging additional trips.

Ride-hailing could reduce VMT by enabling ridesharing.  Ridesharing (carpooling) with individually owned vehicles has been little used in the United States because of the low probability of two individuals regularly going on round trips to and from the same place at the same time.  Ridesharing offered by ride-hailing companies is significantly less constrained because it is arranged dynamically by trip segment and enabled by widely available mobile apps.   However, thus far most ride-hailing trips are for solo riders.

Policies could encourage climate benefits (e.g., by encouraging ridesharing) and minimize disbenefits (e.g., by integrating with rather than substituting for mass transit). Policy in this arena is as nascent as ride-hailing itself.