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NCHRP Web-Only Document 146: Replacement Processes for Light Emitting Diode (LED) Traffic Signals 1 CHAPTER 1 BACKGROUND Effective January 2006, the Department of Energy legislated that signal manufacturers may only manufacture traffic signals that meet ENERGY STAR (2003) power requirements, effectively requiring the use of light-emitting diodes (LEDs) in traffic signal heads. In the absence of standards for maintenance of LED traffic signals, transportation agencies face a huge challenge in defining the life expectancy and creating their operational budgets for maintenance of LED traffic signals. As an initial step in developing maintenance guidelines for LED traffic signals, the National Cooperative Highway Research Program (NCHRP) established Project 20- 7/246, "Replacement Processes for Light Emitting Diode Traffic Signals," to investigate methods for determining when LED traffic signal heads should be replaced, and to discuss possible specifications for LED traffic signals to maximize reliability and minimize maintenance costs. A recently-published NCHRP synthesis report, "LED Traffic Signal Monitoring, Maintenance, and Replacement Issues" (Urbanik, 2008), provides very useful background information to the reader. Urbanik (2008) reviewed the results of a survey conducted by the Institute of Transportation Engineers (ITE) in 2006, of transportation agencies regarding their experienced and practices with LED traffic signals. In general it was found that most agencies did not have a systematic replacement program for LED signal modules, nor was funding in place to monitor and (when necessary) replace modules not performing adequately. Some agencies have established replacement programs whereby modules are to be replaced on a group basis after a number of years in service, but the replacement periods can range from five years to longer periods depending upon the assumptions made by each agency. Urbanik (2008) also reported that one state agency (Louisiana Department of Transportation and Development) specified the use of light output monitoring in LED traffic signal modules, but that there were no modules available meeting such specifications. Because LED traffic signal module failure modes are very different from those of incandescent traffic signal modules, and because the expected operational lifetime of LED modules is so much longer than the operating life of incandescent lamps used in traffic signals, there is a lack of national consensus regarding the best practices for LED traffic signal replacement and for monitoring of signals. The objective of the present project is to identify some of the factors that are related to LED traffic signal module failure, and to discuss some of the steps that might be taken by transportation agencies in the maintenance of LED traffic signal systems.
