Chapter 2: U.S. Transportation System

Chapter 2: U.S. Transportation System

Boat transporting automobiles
Matthew Chambers

Environmental Sustainability

The USDOT has set environmental sustainability as one of the strategic goals in its Strategic Plan for FY2010FY2015. This chapter examines the environmental impacts of transportation as well as energy consumption and prices.

Environmental Impacts of Transportation

Greenhouse gas (GHG) emission measured by carbon dioxide has been recognized as one of the main sources of climate change.1 After reaching a peak in 2007, U.S. energy-related GHG emissions began to decline and decreased by 836 million metric tons, or 10 percent, in 2009 (Table 5-1: U.S. Energy-Related Greenhouse Gas Emissions by End-Use Sector). Between 2007 and 2009, the industrial sector had the highest decrease (16 percent) among the sectors that generate energy-related GHG emissions, followed by the electric power sector (11 percent decrease) and the transportation sector (9 percent decrease). In 2009, the percentage shares of total GHG emissions generated by the residential/ commercial, transportation, and industrial sectors were 40, 26, and 34 percent, respectively. In addition, GHG emissions from electric power, used in all the aforementioned sectors, amounted to 40 percent of total GHG emissions.

GHG emissions generated by passenger cars and light trucks were more than emissions generated by any other transportation mode, including medium and heavy trucks, aircrafts, rail vehicles, ships, and buses. Every year from 2004 to 2008, passenger cars and light trucks generated more than 60 percent of GHG emissions from domestic transportation, compared to medium and heavy trucks, which generated around 20 percent of GHG emissions from domestic transportation each year (Table 5-2: Greenhouse Gas Emissions by Mode). An additional 33 percent of GHG emissions was generated by passenger cars, 9 percent by aircraft, 3 percent by rail, 2 percent by ships, and 1 percent by buses. The domestic transportation sector decreased its GHG emissions by 110 million metric tons from 2007 to 2008. From that total, 38, 35, 16, and 16 million metric tons were from trucks, passenger cars, aircraft, and ships, respectively.

Since 2004, other air pollutants, such as carbon monoxide (CO), nitrogen oxides (NOx), volatile organic compounds (VOC), and sulfur dioxide (SO2), generated by on-road motor vehicles have decreased, although the transportation sector remains one of the main polluting sources. From 2004 to 2008, more than 50 percent of CO was generated by motor vehicles on highways, while more than 30, 20, and 1 percent of NOx, VOC, and SO2 were generated by on-road motor vehicles (Table 5-3: Transportation Air Pollutant Emissions from On-Road Mobile Sources). Improvements in vehicle technologies and enforcements for reducing emissions have produced positive results. The amount of air pollutants generated by on-road motor vehicles declined much faster than other pollution sources. For example, CO generated by motor vehicles decreased from 53 million tons in 2004 to 39 million tons in 2008, which was a 26 percent reduction. Over the same time period, CO generated by all sources decreased by only 22 percent.

As shown in the recent Deepwater Horizon oil spill in the Gulf of Mexico, an oil spill can have serious impacts on the environment and the regional economy, especially where consumer goods are shipped to market via water channels. In 2005, nearly 10 million gallons of oil were spilled from vessel and nonvessel sources, and 8 million gallons were a result of Hurricane Katrina. In 2007 and 2008, slightly more than 700,000 gallons of oil were spilled, which was less than half of the amount that was spilled in 2004 (Table 5-4: Volume of Oil Spills from Facilities by Source).

Energy Consumption and Prices

This section provides information on energy consumption, particularly petroleumrelated consumption, by the transportation sector and describes changes in fuel prices.

Energy Consumption

In the United States, petroleum products are the main energy source for operating 256 million motor vehicles,2 although the share of petroleum products used for transportation has gradually decreased from 97 percent in 2004 to 94 percent in 2009. In addition, the share of natural gas used increased from 2 percent in 2004 to nearly 3 percent in 2009 (Table 5-5: Energy Consumption by the Transportation Sector). Compared with other sectors, such as industry, commercial, and utility, the transportation sector used about 71 percent of petroleum products in 2009 (Table 5-6: U.S. Petroleum Use by Sector).

In 2008, 86 percent of petroleum products were consumed by on-road motor vehicles, 8 percent by aircraft, and 4 percent by ship and boats (Table 5-7: Energy Consumption by Mode of Transportation).3 For motor vehicles, passenger cars consumed 66 percent of fuel products, while trucks and buses used 20 percent of fuel products. From 2007 to 2008, fuels used by ships and boats decreased by 22 percent due to decreased water freight transportation (Table 3-7: U.S. Ton-Miles of Freight). In addition, consumption of aircraft and motor vehicle fuels decreased by 5 and 3 percent, respectively.

Energy Intensity and Efficiency

For motor vehicles, energy intensity is defined as the amount of energy required for motor vehicles to travel 1 mile, while energy efficiency measures the number of miles that a vehicle can travel per gallon of gasoline or diesel.4 Declines in motor vehicle energy intensity can be used as a proxy for representing improvements in energy efficiency. From 2004 to 2008, energy intensity decreased by double-digit percentages for light-duty trucks, buses, aircraft, and railway vehicles used by Amtrak. For example, the energy intensity for transit buses decreased by 18 percent. These decreases indicate improvements in bus energy efficiency after transit buses switched to use natural gas (Table 5-8: Energy Intensity by Passenger Mode). However, energy intensity for passenger cars barely changed during the same period.

Although the Corporate Average Fuel Economy (CAFE) standards enforced by the USDOT for passenger cars have not changed since 2004, the energy efficiency for domestic-produced and imported new vehicles is consistently improving. In 2010, the energy efficiency for new passenger cars was 33.8 miles per gallon, which was much higher than the level of efficiency (27.5 mi/gallon) required by CAFE (Table 5-9: Average Fuel Efficiency of U.S. Passenger Cars and Light Trucks). Despite gains in the energy efficiency of new cars, energy intensity and average fuel efficiency for all U.S. passenger cars has not changed since 2004. This stagnation can likely be attributed to suppressed new car sales and the increased average age of vehicles now on the road. Energy efficiency and intensity measures should eventually improve as older vehicles are retired.

Hybrid or Alternative Fuel Vehicles

New hybrid vehicle sales have increased sharply in the United States since 2004, helping reduce the use of foreign-produced oil and pollution. In 2007, the number of new hybrid car sales reached a peak of 353,000 vehicles, 5 percent of total new passenger car sales.5 In 2008 and 2009, sales of hybrid vehicles declined along with total vehicle sales, but in 2009, hybrid vehicles remained at a relatively high level of about 290,000 vehicles (Table 5-10: Hybrid Vehicle Sales in the United States).

As shown in figure 5-11, Alternative Fuel Vehicles in Use, alternative-fuel vehicles are in use throughout the United States. For example, in 2009, more than 100,000 alternative-fuel vehicles were in use in California and Texas, while an additional 10 states (Arizona, Florida, Georgia, Illinois, Michigan, North Carolina, New Jersey, New York, Ohio, and Virginia) had more than 17,300 alternative-fuel vehicles in use.

Fuel Prices

In the 2000s, oil prices as well as gasoline prices fluctuated and rose to a relatively high level overall. The price of fuels used by aviation, highway, and railroad all rose to above $3 per gallon in 2008 and then declined thereafter.6 From 2004 to 2008, prices for aviation and highway gasoline increased 70 to 80 percent, while jet fuel kerosene, highway diesel, and railroad diesel increased from 150 to 190 percent. In 2009, prices for aviation and highway gasoline decreased by 25 to 28 percent, while prices for diesels dropped by more than 40 percent. (Table 5-12 and Figure 5-12: Fuel Prices; and Table 5-13: Sales Price of Transportation Fuel to End-Users.)

1 For more information, see the U.S. Environmental Protection Agency's website on Atmospheric Changes, available at as of January 2011.

2 See chapter 2 (State of Good Repair) for the number of motor vehicles in the United States.

3 Data for motor fuel used by transit are unavailable for 2008.

4 See the definition from the U.S. Department of Energy, Energy Information Administration, available at as of November 2010.

5 For total new passenger car sales, see U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, National Transportation Statistics, table 1-16, available at, as of November 2010.

6 U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, National Transportation Statistics, table 3-8, Sales Price of Transportation Fuel to End-Users, available at, as of November 2010.