WyoTraveler wrote:
It is measured at the fog line. When truckers see the sign and if low they take the center.
I'm in the profession. They measure at the smallest clearance. Typically, it's at the center but it can vary. If there is a curve, it likely isn't the center. Also, the bridge beams are rarely perfectly level as they match into the grade on the crossing roadway.
No you don't post the exact height or someone like the OP would take off thier air/con. When you are going down the road, the springs bounce up and down. When they hit a bump, the air/con would be 13'1" above the pavement. You reduce the posted measurement to give a little margin for error.
If we repave, we remeasure and put up a new sign.
Your best bet is to back up or turn around but if you must proceed eyeball it to find the high side of the bridge and drive on the shoulder on that side.
