Appendix A: Overhead Sign LightingAnchor: #i998758
Section 2A.08 of the 2003 Texas MUTCD states that “all overhead sign installations should use retroreflective materials, unless an engineering study shows that illumination is needed.”
In 1993, an all-districts memorandum stated that sign lighting is not required for overhead signs fabricated with Type C (high intensity) sheeting, except in areas where sign sight distance or geometric conditions warrant their use.
Recent changes in vehicle headlights have reduced the amount of light reaching overhead signs. This reduction requires that sign sheeting have higher retroreflectivity to maintain the same level of brightness.
In 2003, a change in the Traffic Control Standard Sheets established Type D sheeting (microprismatic) as the standard sheeting for overhead signs.Anchor: #i998783
Standard designs for overhead sign lights are shown in the Traffic Control Standards Sheets (see Chapter 1 for a list of Traffic Control Standard Sheets).Anchor: #i998793
When To Use Lighting
Sign lighting is generally not needed when all of the following criteria are met:
- The sign legend is fabricated from Type D (microprismatic) material.
- The sign is located in a rural environment.
- The height to the bottom of the sign is 20 ft or less.
- The sign and the area 650 ft upstream of the sign are located on continuous tangent alignment with a constant grade.
See Figure A-1 for further explanation and illustration of above.
Figure A-1. Horizontal Sign Cone.
When a sign does not meet all of these criteria, the flow chart in Figure A-2 should be used to determine if sign lighting is needed.
Sign lighting may also be appropriate in other situations for which the need cannot be specifically quantified. Potential situations where sign lighting may be needed include:
- locations where dew frequently covers the sign
- locations with high volumes of heavy vehicles
- areas with significant weaving volumes.
Engineering judgement may identify other situations that require overhead sign lighting.
Figure A-2. Sign lighting flow chart.