Same thing here...on private ground anyway. The log bridges are getting rare now. We took some out completely because of liabilty concerns from hunters and tourists. They were still fairly sound but narrow and with the 4" side rails you mentioned there wasn't much room for error. I see a lot of old railroad flat cars still in use. They seem to hold up pretty well. Bridge approaches were usually more of a problem than the bridges themselves. Especially after a wet winter with high runoffs.