Requirements for Application of Light Emitting Diodes (LEDs) to Traffic Control Signals

Incandescent lamps are presently the major illumination source for traffic signals. They are, however, inefficient compared with 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 that LED signals will meet applicable standards for color and intensity, will not adversely affect the safety or operation of the roadway, and will be economically advantageous. NCHRP Project 5-12 was initiated in response to these needs. 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 digest summarizes the project findings and includes testing results, a discussion of economic analysis, specification guidelines, recommendations for LED use, and suggested future research. The digest will be of interest to those involved in designing and specifying traffic signals.