Watchout for the No Tresspassing sign
Look closely for the "No Trespassing" sign. Yes, I saw it, defaced and all. But I thought I could at least claim stupid if I got caught - which I did (got caught and claimed stupid). Lucky for me, no citations.
While it is also obvious that a railroad bridge is a dangerous place - primarily because there is no place to go if a train comes - this one had strategic escape spots every 50 yards. They were in the form of little 5'x3' balconies, and although quite rusted, would have been better than standing on the tracks if a train came. Lucy for me, I didn't have to find out whether they would support my fat ass.