This synthesis reports on the maintenance and replacement of light-emitting diode (LED) traffic signal modules. It suggests some successful practices to deal with the complexities of the new and evolving LED technology and concludes with suggestions for additional research to resolve outstanding technical issues. It is intended for those currently dealing with the technicalities of evolving LED technology. Although experience is building, LED traffic signals remain an improving product and the uncertainties in the life of LEDs from an economic, performance, and safety perspective are not well understood. This is natural given the nature of LED technology; nevertheless, uncertainties associated with these issues are a major impediment to the development of a sustainable replacement strategy. As the topic panel directed, this synthesis includes the results of a 2006 ITE Task Force survey effort of users and vendors/manufacturers of LED modules. The specific objectives of the synthesis are to familiarize readers with the history of LEDs as replacements for incandescent lamps, to facilitate an understanding of LED issues, to document lessons learned, and to present successful practices in order to minimize future problems. ITE survey information presented includes 75 responses from public agency traffic engineers, consisting of ITE public agency members and AASHTO state traffic engineers, and 6 LED vendors/manufacturers [members of the National Electrical Manufacturers Association (NEMA)]. These survey responses were supplemented by follow-up discussions with various state agency officials who confirmed the initial survey results. A case study details more specific LED information gleaned from the Road Commission of Oakland County, MI's experience with LEDs dating back to 2000.