Bureau of Transportation Statistics

Transportation Trends in Focus

U.S. Department of Transportation

Research and Innovative Technology Administration

June 2009

A Time Series Analysis of Transportation Energy Use 

Per Dollar of Gross Domestic Product

By Peg Young, Ph.D.

TTIF-001

Transportation energy use relative to gross domestic product 

(GDP) has been declining within the past decade. However, 

the total transportation energy consumed (see fi gure 1) shows 

only a more recent decline. To see clearly the long-term 

decline, the seasonal component fi rst must be separated from 

the underlying trendline to observe the long-term trend of that 

energy consumption. Then the ratio of the deseaonalized data 

and GDP can be taken. 

The following graphs and analyses focus on recent trends 

from January 2000 to the present (October 2008). Figure 2 

shows the actual monthly transportation energy use along 

with the underlying trend (noted in red) of that data over this 

shorter time period.

The underlying long-term trend was essentially upward, increasing approximately 5 billion Btu per month, until mid 2007 

when the energy consumption trendline began to turn downward. Occasional slight dips in these consumption changes 

were temporary and proved minor when compared to the 

decline in more recent years.

For the past 8 years, seasonal patterns have exhibited little 

change over time; fi gure 3 depicts the average monthly 

seasonal variation from January 2000 to October 2008. The 

factors indicate that transportation energy consumption tends 

to be the lowest in February (approximately 200 trillion Btu 

below the long-term trend), whereas July and August tend to 

be the highest (approximately 100 and 120 trillion Btu above 

the trend).

Seasonal variation in the data can mask long-term energy 

consumption trends. Removing the effects of seasonality 

from the monthly data reveals both the trend and any remainFigure 1: Total Energy Consumed by 

 Transportation Sector (Trillion Btu),

 January 1990–October 2008

Jan-1990 Jan-1994 Jan-1998 Jan-2002 Jan-2006

1,600

1,800

2,000

2,200

2,400

2,600

Trillion Btu

SOURCE: U.S. Department of Energy, Energy Information Administration, Monthly Energy Review, table 2.5, available at http://www.eia.doe.

gov/emeu/mer/contents.html

Figure 2: Total Energy Consumed by 

 Transportation Sector (Trillion Btu) 

 Actual and Trend,

 January 2000–October 2008

Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08

1,600

1,800

2,000

2,200

2,400

2,600

Total energy consumed by 

transportation sector (trillion btu)

Underlying trend

Trillion Btu

SOURCE: U.S. Department of Energy, Energy Information Administration, 

Monthly Energy Review, table 2.5, available at http://www.eia.doe.gov/emeu/

mer/contents.html and U. S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, special 

tabulations as of February 2009.
BTS Transportation Trends in Focus

2

ing unexplained variation. Figure 4 provides the seasonally 

adjusted monthly data, i.e., the masking effect of seasonality 

has been removed.

The measure of transportation Btu per chained 2000 dollars 

of GDP is a measure of energy intensity for the economy 

and can be used to assess our dependence on oil. Comparing transportation Btu relative to GDP helps determine if the 

changes in GDP explain the changes in transportation energy 

consumption. Because GDP is a quarterly measure,1

 the 

transportation Btu (actual and seasonally adjusted values) are 

converted to quarterly values, as shown in fi gure 5. 

1

 Gross domestic product data available at the U. S. Department 

of Commerce, Bureau of Economic Analysis, http://www.bea.gov/

newsreleases/national/gdp/gdpnewsrelease.htm

Quarterly GDP, which is seasonally adjusted, is divided into 

the seasonally adjusted quarterly transportation energy consumption. The results are provided in fi gure 6, which shows 

that transportation energy consumption has been declining 

relative to GDP. The decline steepened beginning in the third 

quarter of 2007, when the cost of fuel rose dramatically.

Figure 3: Average Monthly Seasonal Factors for Total 

 Energy Consumed by Transportation Sector

 (Trillion Btu), January 2000—October 2008

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

-250

-200

-150

-100

-50

0

50

100

150

Deviation from trend

SOURCE: U. S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, 

special tabulations as of February 2009.

Figure 4: Total Energy Consumed by Transportation

 Sector (Trillion Btu) Seasonally Adjusted,

 January 2000–October 2008

Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08

1,600

1,800

2,000

2,200

2,400

2,600

Trillion Btu

SOURCE: U. S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, 

special tabulations as of February 2009.

Figure 5: Quarterly Energy Consumed by 

 Transportation Sector (Quadrillion Btu) 

 Actual and Seasonally Adjusted,

 1st Quarter 2000–3rd Quarter 2008

Q1 00 Q1 01 Q1 02 Q1 03 Q1 04 Q1 05 Q1 06 Q1 07 Q1 08

5.8

6.0

6.2

6.4

6.6

6.8

7.0

7.2

7.4

7.6

Transportation energy consumption 

(quadrillion Btu)

Transportation Energy Consumptionseasonally adjusted

Quadrillion Btu

SOURCE: U. S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, 

special tabulations as of February 2009.

Figure 6: Quarterly Energy Consumed by 

 Transportation Sector /GDP 

 Seasonally Adjusted, 

 1st Quarter 2000–3rd Quarter 2008

Q1 00 Q1 01 Q1 02 Q1 03 Q1 04 Q1 05 Q1 06 Q1 07 Q1 08

2.0

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

Quadrillion Btu/ billions of chained 2000 dollars

SOURCE: U. S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, 

special tabulations as of February 2009.

NOTE: Btu = British thermal unit. The average heat content 

of motor gasoline is 129,024 Btu per gallon. One quadrillion 

Btu is equivalent to the heat content of 7.75 billion gallons of 

motor gasoline.