After a 2-year interruption to a long-term upward trend, the 

number of vehicle-miles traveled (VMT) on the Nation’s highways appears to have resumed a pattern of upward growth in 

2009. While VMT rises and falls seasonally, the years 2007 

and 2008 showed signifi cant monthly declines in VMT after the 

effects of seasonal fl uctuations were extracted from the data. 

Vehicle-miles traveled by cars, trucks, and buses on public 

roads are a key measure of roadway use.1

 Monthly estimates 

of VMT, produced by the Federal Highway Administration, 

can illustrate when changes occur in the patterns of the data, 

in contrast to annual estimates that may not reveal turning 

points. However, when viewed monthly (as seen in fi gure 1), 

consistent seasonal fl uctuations tend to dominate the pattern 

of VMT historical data, making it diffi cult to determine when 

turning points occur.

1

 A vehicle mile traveled is a measurement of one vehicle traveling one 

mile regardless of the number of occupants in that vehicle.

Transportation Trends in Focus

RITA Bureau of Transportation Statistics

April 2010

Upward Trend in Vehicle-Miles Resumed During 2009

A Time Series Analysis

By Peg Young, Ph.D.

TTIF-003

Figure 1: Vehicle Miles Traveled (billions), 

 July 1990–December 2009

July

1990

July

1992

July

1994

July

1996

July

1998

July

2000

July

2002

July

2004

July

2006

July

2008

100

150

200

250

300

Billions of miles

SOURCE: U.S. Department of Transportation, Federal Highway Administration, Traffi c Volume Trends, http://www.fhwa.dot.gov/ohim/tvtw/

tvtpage.cfm.

Figure 2: Monthly Seasonal Factors for Vehicle Miles

 Traveled (billions), July 1990–December 2009

Jan Feb Mar April May June July Aug Sept Oct Nov Dec

−40

−30

−20

−10

0

10

20

30

Deviation from trend

SOURCE: U.S. Department of Transportation, Federal Highway 

Administration, Traffi c Volume Trends, http://www.fhwa.dot.gov/ohim/

tvtw/tvtpage.cfm and U.S. Department of Transportation, Research and 

Innovative Technology Administration, Bureau of Transportation, special 

tabulations.

About the Transportation Trends in Focus Series

The Transportation Trends in Focus series reports on 

the underlying trends in key transportation data. Using 

a variety of statistical analysis techniques, these reports 

examine recent trends, seasonality, and pattern shifts 

that the data reveal. This report looks at recent shifts 

in the long-term upward trend in monthly U.S. vehiclemiles traveled (VMT).
BTS Transportation Trends in Focus

2

Underneath the regular seasonal repetition, an upward trend 

existed in the growth of VMT for much of the period since 1990 

(fi gure 2). However, the most recent years may be indicating 

a change in that growth pattern. Does a slowdown exist, and, 

if so, when did it start? Has the decline ended? Has upward 

growth resumed? A more detailed analysis of the trend data 

can help answer these questions.

The pattern of the VMT data over time can be described in 

terms of three components: trend, seasonal, and irregular. To 

observe the underlying trend, the data series can be statistically decomposed to allow removal of the seasonal component.2

 

As seasonality changes little from year to year, it is appropriate to calculate the “fi xed” seasonality to quantify the average 

variation for each month of the year as compared to the longterm trend. Figure 2 shows that the summer travel months of 

May through August result in higher than average VMT values, 

while the winter months, November through February, result in 

lower than average VMT values. 

Once the seasonal component has been removed (referred to 

as seasonal adjustment), the long-term trend, along with any 

remaining irregular components, of the VMT data becomes 

clearer. Figure 3 provides a plot of the seasonally adjusted 

VMT data over time. The upward growth of VMT seems to 

2

 Statistical decomposition of the VMT time series is calculated through 

STAMP (Structural Time Series Analyser, Modeller and Predictor) 

software. For more information on the software, go to: http://www.

timberlake.co.uk/.

level off around 2005 to 2007, after which VMT appears to decline, starting around November 2007, but leveling off around 

March 2008. 

Even with seasonality removed, it is diffi cult to ascertain 

without further analysis whether the summer months of 2009 

portrayed an increase or a continuation of the leveling off. 

The irregularity of the seasonally adjusted series in the data 

can be statistically removed to show only the smoother, 

long-term trend. This yields, in fi gure 4, the statistical component that represents the underlying trend for the more recent 

years.3

 As can be seen in the graph, the trend shows a strong 

upward growth, with an average increase of approximately 350 

million VMT per month, until June 2004. The monthly average 

increase in the trend then slowed to approximately 200 million VMT per month from July 2004 through November 2007. 

This slowdown may possibly be attributed to the volatility in 

gasoline prices. The major drop in the trend occurred around 

December 2007, which coincides with the beginning of the 

current recession. From December 2007 through June 2008, 

VMT declined at a rate of approximately 1,200 million (1.2 

billion) per month. From July 2008 through December 2009, 

VMT seems to show signs of resuming its upward growth, at 

an average monthly increase in the trend of 200 million VMT.

3

 Only the last 9 years are shown so the reader can observe the recent 

major drop in VMT more clearly.

Figure 3: Vehicle Miles Traveled—Actual and

 Seasonally Adjusted, 

 July 1990–December 2009

0

50

100

150

200

250

300

July

1990

July

1992

July

1994

July

1996

July

1998

July

2000

July

2002

July

2004

July

2006

July

2008

Billions of miles

VMT (billions)

VMT (billions) seasonally adjusted

SOURCE: U.S. Department of Transportation, Federal Highway 

Administration, Traffi c Volume Trends, http://www.fhwa.dot.gov/ohim/

tvtw/tvtpage.cfm and U.S. Department of Transportation, Research and 

Innovative Technology Administration, Bureau of Transportation, special 

tabulations.

Figure 4: Vehicle Miles Traveled (billions)—

 Actual and Trend, 

 January 2001–December 2009

100

125

150

175

200

225

250

275

300

VMT(billions) actual

VMT (billions) trend

Jan

2001

Jan

2002

Jan

2003

Jan

2004

Jan

2005

Jan

2006

Jan

2007

Jan

2008

Jan

2009

Billions of miles

SOURCE: U.S. Department of Transportation, Federal Highway 

Administration, Traffi c Volume Trends, http://www.fhwa.dot.gov/ohim/

tvtw/tvtpage.cfm and U.S. Department of Transportation, Research and 

Innovative Technology Administration, Bureau of Transportation, special 

tabulations.