There are two issues to consider for vertical signing: the clearance for overhead structures and the vertical clearance for overhead sign supports.

Overhead Bridge Structures.

For information on how to measure and sign vertical clearances for overhead bridge structures, see the

Signs and Marking Volume

of the Traffic Operations Manual, Chapter 6, Section 3.

Overhead Sign Supports.

Regarding overhead sign supports, the following is from the Texas MUTCD, Section 2A.18:

Overhead signs shall provide a vertical clearance of not less than 17 ft 6 in to the sign, light fixture, or sign bridge, over the entire width of the pavement and shoulders except where a lesser vertical clearance is used for the design of other structures. The vertical clearance to overhead sign structures or supports shall not be greater than 1 ft in excess of the minimum clearance of other structures.

In special cases it may be necessary to reduce the clearance to overhead signs because of substandard dimensions in tunnels and other major structures such as double-deck bridges.

Overhead sign structures are not required to have clearance signing, even if the minimum clearance is less than 20 ft (see the

Signs and Marking Volume

of the Traffic Operations Manual, Chapter 6, Section 3).