You can cross on those tiny railways. One at a time.
I've actually just tested it, and if you get caught on those things, you're in the deep end.
EDIT: Of course, while this style of play amuses me to no end, it would probably get blacklisted by most people on Battle.net. I promise my next map will have more maneuverability...
But I am not remaking a Lost Temple for War of the Three Hammers. :P