Well, the MOST eco-friendly means of travel would be by FOOT or HORSE or BICYLE, or SAILBOAT !! ;))
BUT, Trains are more eco-friendly than the auto and aircraft. As Rango points out, highways eat INCREDIBLE amounts of land... here on the San Francisco Peninsula, we have THREE major North-South freeways (101, 280, 1) of 12-8 lanes width running parallel to each other in an area only 30 miles wide! Even THIS massive construct of concrete and asphalt is overcrowded and falling apart.
There are Two International Airports that both eat up a few hundred acres and are overcrowded... along with 2 closed Naval Air Stations and 6 municipal airports. MORE area eaten up by inefficient transit, and OFTEN uninhabitable because of old practices regarding fuel and oil.
INTERESTINGLY, CalTrain runs up and down the peninsula (75 mile route)... It is efficient, faster than a car even when it's NOT rush-hour, and it's RIDERSHIP has doubled over the last decade.
The Altamont Commuter Express (ACE) train runs 86 miles from Stockton to San Jose ("affordable" suburbs to the Silicon Valley JOBS): it is also faster than driving, and is CERTAINLY more comfortable and relaxing.
Now consider each train consumes ABOUT as much diesel-fuel as 2 commuter BUSSES... yet it will carry 400+ passengers as opposed to 80 passengers... sounds more eco-friendly to ME.
Each state needs to pressure their Class 1 RR to upgrade trackage... push Amtrak to increase routes, OR create their OWN regional RR's to serve major Amtrak routes, AND fight to get drivers out of their CARS for certain rides.
I understand there are SOME things a train JUST can't do, areas it JUST can't service... my brother's ranch up in the mountains is CAR / TRUCK only. BUT, when I go to visit, I take the ACE to Stockton and then catch a ride the last 70 miles.