(2) In the USA “Power plants are the nation’s largest source of carbon dioxide emissions from energy consumption, contributing 40 percent of emissions from energy sources in 2005, Passenger vehicles are the next largest source, contributing 20 percent of emissions. Other transportation sources contribute an additional 13 percent of emissions.” .... “Passenger vehicles are responsible for about one-fifth of all carbon dioxide emissions from energy consumption and 60 percent of the carbon dioxide emissions from the transportation sector.”
State and National Trends in Carbon Dioxide Emissions Since 1990. Environment Colorado Research & Policy Center.