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CHAPTER ONE
INTRODUCTION
BACKGROUND of replacement, may lead to LED signal modules remaining
in service after falling below desirable performance levels
Light-emitting diode (LED) traffic signal modules were first unless the owning agency has an appropriate replacement
widely used in the 1990s. An LED signal module provides strategy.
significant energy savings relative to an incandescent lamp,
and the light source has a much longer service life. LEDs are
now being implemented on a widespread basis and will see SYNTHESIS OBJECTIVE
increased use as a result of the Energy Policy Act of 2005
(EPACT 2005). There are, nevertheless, concerns regarding This synthesis reports on current practices for operating, mon-
monitoring, maintenance, and replacement of LED signal itoring, maintenance, and replacement of LED traffic signal
modules. These concerns are centered on several factors. modules. It reviews research and documents national and
It should be noted that many of the problems associated with international standards and practices pertaining to operating,
LED traffic signal modules were the result of early implemen- monitoring, maintenance, and replacement of LED traffic
tations. As will be discussed in more detail, the ITE standards signal modules. The synthesis includes the results of a 2006
have gone through a major revision based on early experience Institute of Transportation Engineers (ITE) survey consisting
and the improvements in LED technology. The traffic signal of 75 responses from users and manufacturers of LED mod-
head application of LED technology is still in a process of ules. The specific objectives of the report are
continual improvements as a result of the increasing population
of installed LED traffic signal modules, longer experience, · Familiarize the reader with the history of LEDs,
and competition for business. · Facilitate an understanding of the issues associated with
LEDs,
Whereas incandescent lamps fail in a catastrophic manner, · Document lessons learned from the experiences of others,
LED signal modules generally lose luminous intensity on a and
gradual basis, creating uncertainty over when they should be · Present successful practices to minimize future problems.
replaced. LEDs are driven by electronics, which make detect-
ing failures more complex. ORGANIZATION OF REPORT
Many LED signal modules were initially financed outside of The report is organized into three additional chapters plus two
the transportation agency as an energy conservation incentive. appendixes. Chapter two provides an overview of current
This has led to some challenges regarding replacement. Once practices. Chapter three provides examples of successful prac-
installed, the cost burden for replacing LED signal modules tices. Chapter four provides conclusions and suggestions for
typically lies with the transportation agency. The gradual further research. The appendixes contain the results of the two
reduction of LED light output, combined with the higher costs 2006 ITE surveys, one of users and the other of vendors.
