http://steamcommunity.com/sharedfiles/filedetails/?id=582547937
http://steamcommunity.com/sharedfiles/filedetails/?id=582547889
You can see in these screenshots I took (actually not see, but the piece is there) a small, almost invisible track on the ground, that has a speed limit of 24 kmph. After a lot of clicking i managed to delete it. The only way to detect such a thing in game is that you see that your trains slow down for no reason.
http://steamcommunity.com/sharedfiles/filedetails/?id=582547956
Also, sometimes trees grow inside rivers 😛 :D:D:D