Tailpipe greenhouse gas (GHG) emissions from transportation sources account for approximately 29 percent of total U.S. GHG emissions, and over 5 percent of global GHG emissions. Including other life cycle processes–such as the extraction and refining of fuel, the manufacture of vehicles and the construction and maintenance of infrastructure–the U.S. transportation sector accounts for almost 8 percent of global GHGs. The majority of transportation's operating emissions, totaling 58 percent, come from light-duty vehicles, followed by freight trucks at 20 percent and aircraft at 12 percent. Between 1990 and 2008, GHG emissions from U.S. transportation increased 22 percent, while emissions from all other sectors increased by roughly 11 percent. The Intergovernmental Panel on Climate Change (IPCC) estimates that in the absence of additional climate policies to reduce GHG emissions, baseline global GHG emissions from human sources will increase between 25 percent and 90 percent between 2000 and 2030, with CO2 emissions from energy use growing between 40 and 110 percent over the same period.
The strategies to reduce transportation GHG emissions are organized into four major groups. They include strategies to:
|Improve system and operational efficiencies by optimizing the design, construction, operation, and use of transportation networks. The strategies range from anti-idling ordinances to traffic management to congestion pricing. The objective of this group of strategies is to reduce the energy use and GHG emissions associated with a given unit of passenger or freight travel (e.g., person-miles, vehicle-miles, or ton-miles of travel).|
|Reduce travel activity by reducing growth in vehicle-miles traveled. The objective of this group of strategies is to influence travelers' activity patterns, thereby reducing total travel, shifting travel to more efficient modes, increasing vehicle occupancy, or otherwise taking actions that reduce energy use and GHG emissions associated with personal travel.|
|Introduce low-carbon fuels. Petroleum-based fuels account for 97 percent of U.S. transportation energy use. The objective of this group of strategies is to develop and introduce alternative fuels that have lower carbon content and generate fewer transportation GHG emissions. These alternative fuels include ethanol, biodiesel, natural gas, liquefied petroleum gas, synthetic fuels, hydrogen, and electricity.|
|Increase fuel efficiency by advancing and bringing to market advanced engine and transmission designs, lighter-weight materials, improved aerodynamics, and reduced rolling resistance. The objective of this group of strategies is to use less fuel and generate fewer GHG emissions.|