Cool things with wheels since 2006
I think most railway bridges have extra tracks inside the regular ones. I think they are supposed to stop the train going over the side if it derails.
wow, that's a good idea!
Those inside rails are called "Guide Rails" and are there to keep the locomotive and the cars on the bridge in case of a derail. As an engineer when you feel a derail on a bridge the pucker factor goes up by a margin of 12. :-)