Are Singapore trains indoor and/or on highway bridge? Most caltrains stations are open platform. Not sure if you have ever been on a caltrain, it runs between suburban area so anyone can just lay herself on the track at any point.
However, there are some above ground sections, and I think the stations there don't have walls. It's been ten years since I've been there, so things might have changed...
http://en.wikipedia.org/wiki/Safety_on_the_Mass_Rapid_Transi...