George,
Not all the time. I've been in a lot of places where there were no signs telling drivers of low clearnances except at the bridge itself. New York is one of the worst. And that federal 14' standard is BS. If you take I-55 around south Memphis and your trailer is 13'7", your going to hit something. Downtown Chicago is another one. Off the Eisenhower Exsp, you have several low off ramps with no warnings. After 30 years on the road, I've only tagged one bridge. Bridge was listed as 13' 6". Guess what happens when they lay 3 new inches of blacktop on the road...AND DON'T CHANGE THE SIGNS!!! And don't forget what happened north of Seattle when that trucker took out the bridge on I-5. That one is still up for debate. He was permitted to cross the bridge but no one was aware that the bridge was below the restrictions at the fog line. Even the state admitted they screwed up not noting the low clearances on the shoulder.

J Loggans
Vancouver WA