CO₂ emissions from the combustion of fossil fuels in the transportation sector dropped 1.1%, from 1,763.9 million metric tons in 2010 to 1,745.0 million metric tons in 2011.

Transportation activities (excluding international bunker fuels) accounted for 33% of CO₂ emissions from fossil fuel combustion in 2011. Virtually all of the energy consumed in this end-use sector came from petroleum products.

Nearly 65% of the emissions resulted from gasoline consumption for personal vehicle use. The remaining emissions came from other transportation activities, including the combustion of diesel fuel in heavy-duty vehicles and jet fuel in aircraft.

Light duty vehicles (including passenger cars and light-duty trucks) represented 61% of CO₂ emissions, medium- and heavy-duty trucks 22%, commercial aircraft 7%, and other sources 11%.

From 1990 to 2011, transportation emissions rose by 17% due, in large part, to increased demand for travel and the stagnation of fuel efficiency across the US vehicle fleet, EPA said.

Ethanol consumption from the transportation sector has increased from 0.7 billion gallons in 1990 to 12.3 billion gallons in 2011.

The number of vehicle miles traveled by light-duty motor vehicles (passenger cars and light-duty trucks) increased 34% from 1990 to 2011, as a result of a confluence of factors including population growth, economic growth, urban sprawl, and low fuel prices over much of this period. The more recent trend for transportation has shown a general decline in emissions, due to recent slow growth in economic activity, higher fuel prices, and an associated decrease in the demand for passenger transportation.

Commercial aircraft emissions continued to fall, having decreased 18% since 2007. Decreases in jet fuel emissions (excluding bunkers) are due in part to improved operational efficiency that results in more direct flight routing, improvements in aircraft and engine technologies to reduce fuel burn and emissions, and the accelerated retirement of older, less fuel efficient aircraft.

The Inventory of US Greenhouse Gas Emissions and Sinks: 1990-2011 is the latest annual report that the United States has submitted to the Secretariat of the United Nations Framework Convention on Climate Change since it was ratified by the United States in 1992. The treaty sets an overall framework for intergovernmental efforts to address the challenge posed by climate change. EPA prepares the annual report in collaboration with other federal agencies and after gathering comments from stakeholders across the country.

The inventory tracks annual GHG emissions at the national level and presents historical emissions from 1990 to 2011. The inventory also calculates carbon dioxide emissions that are removed from the atmosphere through the uptake of carbon by forests, vegetation, soils, and other natural processes (called carbon “sinks”).