Jakblumule is right on.I've been a trucker for quite a few years and rule of thumb is 13'6" cept for NY & NJ where their marked 1 foot lower than they really are.Chicago and many of the larger cities have many low underpasses.Most have sign posted either 1000' before the pass or right on them.It's a real big pain when posted like 13'0" for a semi,you don't see it until your at the thing,and of course no where to turn around w/ten cars laying on their horns right on your bumper

.Most semi's get in trouble like this from people that give the directions, who don't have a clue we're bigger than their four wheeler (car).Also the height signs are mainly on roads that a semi might visit,so,if off the main roads in the woods/narrow road,lots of overpasses are NOT posted due to lack of truck traffic.....Brian-hope that helps