The Application of Light Emitting Diodes to Traffic Signals

Incandescent lamps are currently the major illumination source for traffic signals. The incandescent lamps used for traffic signals are, however, inefficient compared to other light sources. Maintenance costs are high for these lamps and the light output degrades as the lamp ages. These problems, plus the ever-increasing cost of energy, justify considering other light sources. One alternative is light emitting diodes (LEDs).

Before existing incandescent lamps are replaced by LEDs, it is necessary to show the LED signals will meet applicable standards for color and intensity, not adversely affect the safety or operation of the roadway, and be economically advantageous. NCHRP Project 5-12 was initiated in response to this need. The objective of the research was to determine the feasibility and implementation potential of LEDs. The project found that red and Portland orange (pedestrian) LED signals are currently feasible.

This paper summarizes the project findings and includes testing results, a discussion of economical analysis, specifications guidelines, recommendations for LED use, and suggested future research. It is hoped that the information will be of interest to those involved in designing and specifying traffic signals.