Well, as an ex-railroad engineer, I have to side with JustMe on this one. Rail travel is exceeding dirty. Just about every rail-yard in the US is on the EPA clean up list. The number of train crew that have died from cancer (diesel exposure) or are ill from the exposure is a very long list.
Every mile of rail in the US is a path of toxicity from leaked oil and fuel, grease (tracks are actually greased in many places to reduce wear on curves), and don't even talk about derailments where massive quantities of toxic chemicals get spilled. Example:
http://articles.latimes.com/1991-07-...uthern-pacific
Passenger travel is a tiny percentage of rail usage, but the rail system as used every day is anything but green.