Outside the Northeast Corridor and a route in Pennsylvania from Philadelphia to Harrisburg, all Amtrak trains are powered by diesel locomotives, which emit greenhouse gases and fine particulate matter that can cause health problems.

Amtrak uses a combination of diesel and electric propulsion, depending entirely on the specific route and infrastructure available. On the Northeast Corridor (NEC)—the busy stretch between Boston, New York, and Washington, D.C.—Amtrak operates almost exclusively on electricity via overhead catenary wires. This includes the high-speed Acela and the Northeast Regional. However, for the vast majority of its long-distance routes across the United States, Amtrak relies on diesel-electric locomotives, such as the Siemens Charger or the older GE Genesis. These "diesel-electric" engines don't actually use the diesel to turn the wheels directly; instead, the diesel engine runs a large generator that produces electricity, which then powers electric traction motors to move the train. This is necessary because most tracks in the U.S. (which are often owned by freight companies) are not electrified. So, while you might see smoke from an engine in the Midwest, your ride from NYC to D.C. is likely 100% electric.