Safe:  Your own personal safety should be your greatest concern.  Stay off the tracks and stay back as trains go by.  Defective railroad cars throw brake shoes, rods and contents far from the tracks that can injure or kill you.  Trains also derail, spreading their engines and cars hundreds of feet from the right of way.  A telephoto lens is the best safety investment you can make.  Also, be aware of your surroundings.  Railroads are often located in high crime areas.  Watch who is around you and stay alert.  Go in pairs or groups.  In the worst neighborhoods, leave your car running and be ready to drive off (if you must go there at all).  Take a cell phone with you.

Responsible:  Trespassing on private property is a misdemeanor.  Theft of property is a felony, if the value of the stolen items exceeds $100.  Both local police and railroad police have broad powers to ticket or arrest offenders.  Railroad police, in particular, aggressively enforce trespassing laws on their own right of way.  Stay on public property, or get permission in writing.