Why Focus on the Transportation Sector?
In the United States, transportation is the sector with the highest greenhouse gas (GHG) emissions, emitting 28 percent of U.S. GHG emissions. It attained this distinction in 2016, when it edged out electricity for the first time as electric sector GHG emissions declined.
What Makes the Transportation Sector Different in Terms of Reducing Carbon Emissions?
U.S. transportation is more than 90 percent dependent on oil. The current low price of petroleum products like gasoline and diesel provides little incentive for travelers or shippers to reduce driving, choose more efficient vehicles, or shift transportation modes. About 60 percent of U.S. transportation sector GHG emissions comes from “light-duty vehicles” (cars and light trucks). The remainder comes from heavy-duty trucks and buses, trains, airplanes and ships.
The key success story over the past few decades for restraining transportation GHG emissions has been vehicle fuel efficiency and GHG standards for cars and trucks, which save consumers and truckers money and reduce U.S. oil dependence. Beyond energy efficiency, a key pathway to decarbonizing transportation is through alternative fuels. Electricity, hydrogen, biofuels and ammonia are key options here; importantly, the life cycle emissions from using alternative fuels depend on how the fuels are made. Other key pathways include increasing the use of public transportation, and reducing travel demand (e.g., through changing the design of our communities, or changing how and where we live and work.)
The impact of autonomous vehicles is a wild card that could make transportation decarbonization either much harder or much easier. On the one hand, intelligent vehicles and transportation systems can drive tremendous efficiency gains through improved traffic management, constant speeds, and limited breaking and accelerating, thereby reducing fuel use and emissions. On the other hand, automation can dramatically increase travel demand because more people can be driven than can drive.
Electricity is a key focus for cars and light trucks, and electric vehicle numbers are growing. The success of electrification as a decarbonization strategy depends on the decarbonization of the electric grid. (See electricity sector overview.) Other modes of transportation that need to decarbonize, including heavy trucks, buses, ships, and airplanes, do not lend themselves a easily to electrification, but can be addressed by increasing efficiency, using other low- or zero-carbon fuels and shifting travel and freight movement to less carbon-intensive modes of transport (e.g., by shifting shorter airplane flights to electric-powered rail).
Transportation emissions depend on the interplay of technology innovation, market forces, human behavior and public policy, and public policy happens at the federal, state and local level. Key transportation emission reduction options include continuing to strengthen vehicle efficiency and GHG standards; increasing investment in information technology and lower-emitting vehicles and fuels; and implementing smarter, more transportation-efficient growth and mobility initiatives in our communities.