I was hauling a piece of equipment one time that was slightly over height and was routed and came upon an overpass that was just slightly higher than my load was, I slowed up and got almost up to the bridge and stopped and got out to measure the bridge off the hood of my truck, sure enough it was too low, the city had poured a layer of black top over the existing road and never changed the sign. Called the state that routed me and told them the problem I had and oh yea by the way there are a lot of pissed off drivers behind me lined up for almost a mile and get someone out here to direct traffic, I need to back out of here and it's almost a mile before I can turn around, took only a few minutes to get help but hours to get backed out of the mess. Now I always have someone go ahead to measure overheads for me when I'm hauling over height things and unless its an interstate bridge I never take any height posted as gospel but instead have them measured for me by someone I trust or have a pole on a truck to see if it clears by at least 6 inches before I go under them.