I didn't think this was true, but according to the EPA in 2021 it is
Personal transport road vehicles are the largest category of transportation which is the largest source of greenhouse emissions, accounting for roughly 15% of total us emissions.
The largest sources of transportation-related greenhouse gas emissions include passenger cars, medium- and heavy-duty trucks, and light-duty trucks, including sport utility vehicles, pickup trucks, and minivans. These sources account for over half of the emissions from the transportation sector. The remaining greenhouse gas emissions from the transportation sector come from other modes of transportation, including commercial aircraft, ships, boats, and trains, as well as pipelines and lubricants.