Energy and Emissions in Transportation

World Energy and Emissions

Worldwide, transportation consumes primary energy as follows.

Unless otherwise noted, figures are reported by the IEA Sankey Diagram ¹. The IEA Transport survey ² splits road transportation into travel and freight, and the EIA Global Transportation Energy Consumption review ³ splits road travel into cars, buses, and 2- and 3- wheelers. Energy in cycling assumes 450 billion passenger-kilometers per year ⁴ and 1322 kilojoules primary energy oer kilometer traveled, as determined in our review of short-range transportation. See our reviews of information technology and space travel for energy in those categories. Estimates include energy required to manufacture vehicles and infrastructure for cars, buses, rail, and air travel, as estimated by Chester and Horvath ⁵.

Greenhouse gases from world transportation are estimated as follows.

For each category, energy inputs are as shown in our review of world transportation energy above. The emissions intensity of energy inputs are given by the EPA ⁶, Hanova and Dowlatabadi ⁷, Staffell ⁸, and Fridleifsson et al. ⁹. The emissions intensity of the food input energy into cycling is determined in our review of the emissions of the world food system. Emissions for cars, buses, rail, and air travel include those from manufacture of vehicles and infrastructure, as estimated by Chester and Horvath ⁵.

Lifecycle Energy

Throughout the Transportation section, we generally quote energy figures in terms of the fuel used by the vehicle or the primary energy behind the fuel, while not including the energy required to manufacture and maintain the vehicle and infrastructure (e.g. roads, tracks, etc.). However, the latter values may be significant.

See ¹⁰ for an overview, ¹¹ for the sedan and Boeing 737, and ⁵ for BART, Caltrain, and bus.

An electric car, in a city in which all grid electricity is from renewable or nuclear sources, has much lower greenhouse emissions than a gasoline car, but not zero emissions. The electricity is not truly zero carbon, and there are also emissions in the manufacturing of the vehicle. The latter are typically attributed to industry, rather than transportation, in national accounting.

World Transportation Emissions (PDF)

Worldwide, transportation energy is dominated by petroleum-based fuels, and petroleum will continue to dominate well past 2050.

Sources: EIA ¹² and EPA ¹³.

U.S. Transportation Emissions (PDF)

As is the case worldwide, transportation in the United States is predominately powered by fossil fuels and comes mainly in the form of motor vehicles.

Intercity Transportation

The energy required to move a passenger one kilometer over long distances varies widely both between and within modes. The occupancy rate (percentage of seats occupied by passengers) and efficiency of the vehicle are two key variables that affect performance. In general, though, buses and electric rail tend to be the most efficient systems, while diesel rail such as Amtrak, aviation, and driving are less efficient.

Primary energy is greater than the energy used directly by the vehicle, especially for electric modes. See below for details on aviation and rail, and our analysis of automobiles. For estimates on the energy needs of intercity buses, see the Bureau of Transportation Statistics ¹⁴, John Dunham & Associates ¹⁵, M. J. Bradley and Associates ¹⁶, and Minn ¹⁷.

Commuter Transportation

The energy intensity of major modes of commuting, or other typical travel within cities, varies more within modes than between modes. The most important factor influencing the efficiency of bus and rail systems is the occupancy rate, or the portion of seats that are filled. Generally, transit systems in large, dense cities with heavy ridership are the most efficient.

See our analyses of cars and mass transit for more information. Figures are reported as primary energy.

Transportation Energy Efficiency

Per-mile energy requirements of transportation (PDF)

There is wide variation of energy consumption both between and within different modes of transportation ¹⁴. No particular option is necessarily "the best" in general.

Source: ¹⁸