TxDOT policy is to not use overhead sign lighting unless a sign is positioned in a manner such that vehicle headlamps will not provide sufficient illumination to meet driver luminance needs. Appendix A provides a procedure to determine if sign lighting is needed.

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).

Control cities are key cities located on a freeway route that are used for destinations in freeway interchange signing and in distance signing.

The following table lists the control cities for interstate highways located within Texas. The control cities are identified in Part III — “List of Control Cities for Use in Guide Signs on Interstate Highways,” GSGLC-4 (American Association of State Highway and Transportation Officals, Washington, D.C., 20001). Control cities should be used for all interstate highways. Non-interstate freeways should use the interstate control cities where possible and should use cities of similar population or significance where it is not possible to use the interstate control cities. Any given route should have the same control cities in both directions of travel and the control cities must lie on the intersected route. Additional guidelines for destination names are included in Part 2E of the Texas MUTCD.

TxDOT traffic engineering standard sheets include numerous standard sheets for the design of overhead sign structures and the infrastructure related to the overhead structures (such as foundations, lighting, walkways, etc.). The standard sheets may be downloaded from the TxDOT web site at: .