Vehicle Miles Traveled

Vehicle Miles Traveled (VMT) is the total number of miles driven by all vehicles within a given time period and geographic area. It is used by regional transportation and environmental agencies for planning purposes. VMT is influenced by factors such as population, age distribution, and the number of vehicles per household. However, the greatest factor by far is how land uses are arranged.

A more tangible measure of car use may be per capita VMT, which is the number of miles driven per person per day. For example, residents of an auto-oriented neighborhood in Atlanta (the most sprawling city in America), drive an average of 39 miles per person each weekday, which is 30% more than those who live in the most walkable neighborhood[8].

VMT has increased steadily during the post-war period. However, total U.S. VMT began to plateau in 2004 and dropped in 2007 (and again in 2008) for the first time since 1980, a recessionary year[9].

The Land Use-VMT Connection

For decades, researchers have sought to understand exactly how land use influences VMT. During the 1990’s, a number studies seemed to show that this connection was weak, at best, but these studies suffered from methodology problems and poor data[7]. More recent studies that take advantage of GIS and better data show a stronger link. A landmark 2007 book looked at all the available evidence and concluded that sprawling communities that require car trips to meet most daily needs exhibit 20-40% higher VMT than more compact, mixed-used, and walkable neighborhoods[6].

Studies[7] have shown that the following land use and transportation attributes can significantly reduce VMT, by reducing trip lengths, and encouraging alternatives to driving:

Placing new development in already developed areas, close to population centers, rather than on the suburban fringe or in exurban (rural) areas.
Higher residential densities
Higher retail densities
Connectivity – direct, rather than circuitous, driving and walking connections
A variety of walking-distance destinations, such as groceries, other retail and services, and civic uses
Reduced parking supply, and parking located to the rear of buildings
Frequent, reliable, and comfortable transit service

Statistics

The Federal Highway Administration estimates monthly national VMT with highway traffic volume counts. Presented in a monthly report called Traffic Volume Trends, these data are compiled by each state from a total of “4000 continuous traffic counting locations nationwide”. [1] Changes in traffic volume are revealed by comparing traffic counts with the same month of the previous year. The National Household Travel Survey [2], conducted roughly every 5 years, provides more specific information about VMT and Americans’ driving habits.

According to the U.S. Bureau of Transportation Statistics, monthly VMT data are a good indicator of roadway use; they are used to estimate traffic congestion and air quality. In a nation so dependent on the automobile, VMT also correlates well with economic activity, as well as greenhouse gas emissions. In January 2008, Americans drove a total of 226 billion miles. VMT peaks in summer and is lowest in winter[3].

Overall Rise in Vehicle-Miles Traveled

A steady increase in VMT has been observed over the last several decades. According to the Wall Street Journal, “from 1977 to 2001, the number of miles driven every year by Americans rose by 151% — about five times faster than the growth in population” [4].

Land use – namely sprawl development – is the main culprit. Americans are living farther from work, school, shopping and basic services. Even in higher density areas, where amenities may be closer to home, the road design can be punishing for pedestrians. It is nearly impossible to walk in areas that cater primarily to motor vehicles. Autocentric street design therefore forces more cars onto roadways, which further impedes walkers and bicyclists. The vicious cycle continues and local governments turn to the only “quick fix” that they seem to know: build bigger highways (at enormous taxpayer expense) to accommodate the increased traffic.

Arguably more important than fuel efficiency, Vehicle Miles Traveled directly affects gas consumption, emissions, and traffic patterns. A Prius owner who makes multiple, unnecessary trips and has a long work commute is no more virtuous than a Hummer driver who works close to home. Congress has addressed fuel efficiency. In December 2007, after 20 years of inaction, lawmakers finally mandated that Corporate Average Fuel Economy (CAFÉ) standards be improved to 35 miles per gallon by the year 2020. This landmark legislation was achieved only after years of resistance by the automobile industry and a Democratic revolution in the 2006 mid-term elections. However, changes in VMT have historically overtaken improvements in fuel efficiency. Recently, the threat of global climate change has induced policymakers to consider ways to reduce VMT by, for example, imposing higher gas taxes, curtailing funding for highway expansion, increasing investments in public transit, and limiting sprawl.

Rising Gas Prices, Fewer Miles Driven

Highway VMT dropped from 2007 to 2008 due to higher gas prices and the onset of an economic recession. The federal Department of Transportation reported a decline of 20 billion miles during the January – April period, compared to the same period in 2007. It is unlikely that the high cost of fuel alone will force a steady downward trend in VMT, but it may generate the political will needed for major changes in transportation and land use.

VMT Trivia

A survey commissioned in the 1990’s by the U.S. Department of Energy measured VMT between 1988 and 1994 [5]. Using a representative sample of vehicles, beginning-of-year and end-of-year odometer readings were recorded. The data were then extrapolated to the entire national fleet. Findings included as follows:

– Newer cars are driven more than old cars.
– Minivans were driven more than other cars.
– Teenagers boost miles driven per household.
– Higher income residents drive more than low-income residents.
– Older drivers drive less.

ALSO ON THE LIVABLE STREETS NETWORK

Is Big Environment Ready to Say America is Hooked on Cars? Streetsblog, February 25, 2008.

REFERENCES

[1] Traffic Volume Trends. Federal Highway Administration. US Department of Transportation.
[2] Quick Start Guide, National Household Travel Survey, U.S. Department of Transportation.
[3] U.S. Highway Vehicle Miles Traveled. Bureau of Transportation Statistics. US Department of Transportation.
[4] White, Joseph B. The Next Car Debate: Total Miles Driven. The Wall Street Journal, February 5, 2008.
[5] Vehicle Miles Traveled. Transportation Energy Consumption Surveys. Energy Information Administration, US Department of Energy. Chapter 3.
[6] Ewing, Reid. Growing Cooler: The Evidence on Urban Development and Climate Change. Chicago: Urban Land Institute, 2007.
[7] Lawrence Frank and Company, Inc. Reducing global warming and air pollution: the role of green development in California, prepared for Environmental Defense Fund. 2008.
[8] Frank, Lawrence and J. Chapman. Integrating travel behavior and urban form data to address transportation and air quality problems in Atlanta. Prepared for the Georgia Department of Transportation Georgia Regional Transportation Authority. April 2004.
[9] Puentes, Robert and A. Tomer. The Road Less Traveled: An Analysis of Vehicle Miles Traveled Trends in the U.S., Brookings Institute. December 16, 2008.

PICTURE REFERENCES

Pictures are cited in the order they appear above. Please keep citation style consistent.
[1] San Francisco traffic. Photo by mathoov via Flickr.
[2] Retail street, Hudson, OH. Photo by Dan Burden via Pedestrian Bicycle Information Center Image Library
[3] US HIghway Vehicle Miles Traveled. Bureau of Transportation Statistics. US Department of Transportation. May 2008.
[4] Gas price June 2008, Massachusetts. Photo by Svadilfari via Flickr

KEYWORDS

VMT, mode shift, trip reduction, connectivity, 4 D’s,

Zhuo Yao, Ph.D.

Vehicle Miles Traveled – http://streetswiki.wikispaces.com/Vehicle+Miles+Traveled