If you’re traveling long distance, say from Chicago to LA, walking is the most eco-friendly way you can go, but it’s not really an option. (And most of us aren’t fit enough to bicycle there, either.) So between cars, planes and trains, which is the greenest way to travel? If BTUs (British Thermal Units) are any measure – and in fact, BTUs are a good surrogate measure for carbon footprint – then train travel is among the most energy efficient, Earth-conscious ways to get there.

Here are a few ways that Amtrak, America's passenger rail service, has made changes that conserve energy.

• The U.S. Department of Energy (DOE) has reported that Amtrak – on an energy-consumed-per-passenger-mile basis – is 17 percent more energy efficient than commercial airlines. According to DOE's Transportation Energy Data Book, Amtrak energy intensity was 2,935 British Thermal Units (BTUs) per passenger-mile and commercial airlines were 3,587. Commuter rail was 2,751 and automobiles were 3,549 BTUs. The DOE figures are from calendar year 2003, the latest available.
• Unlike commercial aviation, which mostly uses highly refined jet fuel, Amtrak uses diesel fuel produced at a higher volume per barrel of crude oil and electricity produced in the Northeast from a variety of fuels.
• Amtrak has an operating policy to reduce the amount of time that a powered locomotive is idle and is installing a new automatic shut-off system in its diesel locomotive fleet to limit idling.
• Increased use of dynamic braking, which involves the electric traction motors in locomotives, provides resistance to the rotating wheel axle. This method of slowing trains is more fuel-efficient than braking with power applied.
• Acela Express high speed trains and other new and remanufactured electric locomotives have enabled Amtrak to reduce energy consumption by up to eight percent through the use of a regenerative braking system. This braking system returns electric energy overhead to the catenary power system and replaces some of the electrical energy consumed.
• Amtrak recently introduced 80 new vehicle carriers for the Auto Train. These are substantially lighter than the ones they replaced and have helped reduce annual diesel fuel usage by about 640,000 gallons – while carrying more vehicles.
• Last year, Amtrak substituted electric locomotives for diesel locomotives on the Keystone Corridor between Philadelphia and Harrisburg, Pa., improving fuel efficiency and schedules.

To find out more about Amtrak's green initiatives, including their partnership with Carbonfund.org to offset the carbon footprint from Amtrak travel, go to the Amtrak and the Environment page at Whistle Stop.