Two quick searches found that some trains allow people to get off and grab a quick smoke at some stations. While another search turned this up:

"Thank you for contacting Amtrak.
To answer your inquiry, smoking is prohibited entirely in all areas of all non-overnight trains, as well as on the Coast Starlight and the Twilight Shoreliner.
On other long distance overnight trains, cigarette smoking ( only ) is permitted at designated times either in lounge areas or in a specially designated area only-- not in coaches, sleepers, dining cars or any other area. The crew on each train will announce the designated lounge area smoking times.
See the "Services" section listed for each train in our national timetable for more specific information regarding the particular train you wish to travel on. As information, cigarettes are not sold on board trains that do not permit smoking.
We apppreciate this opportuniy to be of service.
---Customer Service"

Just do a Google with the name of the train line, like: "Amtrak smoking policy".
9ski9 Reviewed by 9ski9 on . Smokin on the Train ride has anyone ever taken a train? if so can you smoke on it? im thinking about taking a train to go see my parents. 14hour by train 12-13 by car so i think the train would be better less mileage on my car and i could walk around. BUT i want to smoke some bud while on the train!!! what if i mix it with tobacco? anyone have any ideas???? Rating: 5