I believe that there were some rather vicious gangs that rode/ or ride the rails I think they were called Freight Train Riders of America. Don't know how active they are now but since railroads are concerned about people that break into trains and steal TV's stereos and other cargo and assault crew members the RR police and train crews would not be very tolerant of people hopping on trains even if they aren't terrorists or thieves. Also they RR police have to keep people off trains so they or their families don't sue them if they get hurt or die on a train.