GHG emissions from transportation accounts for about 27% of GHG emissions in the U.S., second only to electricity generation (31%) (2013 USEPA). Within the transportation sector, light-duty vehicles were the largest category (60%) and medium- and heavy-duty trucks made up the second largest category (23%). From 1990-2013, GHG emissions in the transportation sector increased more in absolute terms than any other sector (i.e. electricity generation, industry, agriculture, residential, or commercial). (U.S. Transportation Sector Greenhouse Gas Emissions 1990-2013, U.S. EPA)
Transportation energy and climate change are closely intertwined since GHG emissions are a directly related to energy consumption. Global transportation energy demand is expected to increase substantially without implementation of aggressive policies, and could potentially be the fastest-growing end-use sector.
For the most part, efforts to meet energy use reduction goals also will reduce transportation’s GHG emissions.