There is often a good reason for "No Trespassing" signs

[ricktas]

Derilict buildings, work-sites, railyards and more. There is a good reason that some places are fenced off and have signs restricting entry.

http://www.news.com.au/breaking-news/shock-for-photographer-during-erotic-shoot/story-e6frfku0-1226152470455

[Redbaron]

oops.... hope his injuries weren't anywhere embarrassing - would be hard to explain when he got home!

Conversely, it would be an interesting work cover form to read....

[Kym]

For those that don't know I work in the rail industry and have a bit to do with safety systems.
I am aware of many deaths, injuries and near misses.

Just a reminder...

It is illegal to be in the rail corridor without authorisation (i.e. within the fenced area or 15m from the outermost rail)
It is illegal to shoot photos from rail pedestrian crossing as you are required to cross promptly
If you want top shoot photos at a station, ask the station manager first; you may or may not be allowed to use tripods etc. for safety reasons

This from Queensland (http://www.queenslandrail.com.au/AllStations/Pages/AccesstoQueenslandRailPremises.aspx) has some good information; which applies in principal elsewhere.