Originally Posted by sailingdog
Not true... but 13.5' is important since that is the minimum height required without a posted sign by the Interstate Highway System. Bridges and tunnels with a clearance less than 13.5' have to have a sign posted stating the maximum clearance. You can have taller loads on a trailer, but you have to be much more careful about where you travel.
I think the standard height though is 14', not to say that they aren't usually higher...we can look it up if it's important...(I am also a retired CDL instructor)