I wish both trucks and bridges would give real measurements. I've driven a few 13' trucks under 12' overpasses, without a problem. Someday I'll probably run out of gas in a 12' truck delivering a 13' bridge.
the common issue with the shorter height is road paving with the city not checking the height. I've heard of it happening before in my city. Biggest problem with it that I see is that the city claims no responsibility even when their signs are wrong and win almost all the time if they ever loose.
