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ACKNOWLEDGMENT This work was sponsored by the American Association of State Highway and Transportation Officials (AASHTO), in cooperation with the Federal Highway Administration, and was conducted in the National Cooperative Highway Research Program (NCHRP), which is administered by the Transportation Research Board (TRB) of the National Academies. COPYRIGHT PERMISSION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FMCSA, FTA, Transit Development Corporation, or AOC endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. DISCLAIMER The opinion and conclusions expressed or implied in the report are those of the research agency. They are not necessarily those of the TRB, the National Research Council, AASHTO, or the U.S. Government. This report has not been edited by TRB.
NCHRP Web-Only Document 146: Replacement Processes for Light Emitting Diode (LED) Traffic Signals iii CONTENTS LIST OF FIGURES .................................................................................................................... iv LIST OF TABLES ....................................................................................................................... iv ACKNOWLEDGMENTS .............................................................................................................v ABSTRACT .................................................................................................................................. vi CHAPTER 1 Background ............................................................................................................1 CHAPTER 2 Research Approach ...............................................................................................2 CHAPTER 3 Findings and Applications ....................................................................................3 Research Review and Synthesis...........................................................................................3 Photometric Measurement Techniques ................................................................................9 LED Traffic Signal Failure Modes ....................................................................................17 CHAPTER 4 Conclusions, Recommendations, and Suggested Research .............................26 Conclusions ........................................................................................................................26 Recommendations for Replacement Strategies .................................................................27 Suggested Research ...........................................................................................................31 REFERENCES .............................................................................................................................33
NCHRP Web-Only Document 146: Replacement Processes for Light Emitting Diode (LED) Traffic Signals iv LIST OF FIGURES Figure 1. Luminous efficiency functions for color-normal and protan observers, and spectral distribution from red incandescent and LED traffic signal modules (Andersen, 2002). Figure 2. a) Average reaction times and interquartile ranges for color-normal subjects; b) average reaction times and interquartile ranges for protan subjects (Huang et al., 2003). Figure 3. Block diagram of a typical LED signal module design. Figure 4. Arrays of 2 Ã 20 and 4 Ã 20 LEDs in parallel. Figure 5. Power resistor and smoke residue on nearby LEDs. Figure 6. Defective Schottky diode. Figure 7. Locations of failed LEDs. LIST OF TABLES Table 1. Measured illuminance and calculated luminous intensity values for different measurement distances (red signal module). Table 2. Measured illuminance and calculated luminous intensity values for different measurement distances (green signal module). Table 3. Luminous intensity values estimated from luminance values using luminance test method 1 (red signal module). Table 4. Luminous intensity values estimated from luminance values using luminance test method 1 (green signal module). Table 5. Luminous intensity values estimated from luminance values using luminance test method 3 in an exterior, daytime environment (green signal module). Table 6. Long term annual costs for spot and group replacement strategies for an agency responsible for maintaining 100 signalized intersections, assuming a 7-year expected life. Shaded cells indicate when group replacement is estimated to be more costly than spot replacement. Table 7. Long term annual costs for spot and group replacement strategies for an agency responsible for maintaining 100 signalized intersections, assuming a 10-year expected life. Shaded cells indicate when group replacement is estimated to be more costly than spot replacement.
NCHRP Web-Only Document 146: Replacement Processes for Light Emitting Diode (LED) Traffic Signals v ACKNOWLEDGMENTS The authors acknowledge sponsorship of this research from the National Cooperative Highway Research Program (NCHRP) of the Transportation Research Board. The authors would also like to gratefully acknowledge the City of Los Angeles, the Nebraska Department of Roads, the New Jersey Department of Transportation, the New York State Department of Transportation, and the Wisconsin Department of Transportation for providing traffic signal modules to the project team for evaluation.
NCHRP Web-Only Document 146: Replacement Processes for Light Emitting Diode (LED) Traffic Signals vi ABSTRACT This report documents and presents the results from a study of the photometric requirements, measurement and maintenance of traffic signal modules using light emitting diodes (LEDs). Differences between LED technology and the incandescent lamps used in previous traffic signal modules in terms of photometric performance, color, and failure modes require new approaches to traffic signal maintenance. Findings from a review of literature on human factors and maintenance practices, from a series of laboratory and field measurements of LED traffic signal modules, and from an analysis of the failure mechanisms of traffic signal modules provided by several different transportation agencies, are provided. Based upon these findings and upon an economic analysis with different assumptions regarding LED traffic signal module failure rates, some preliminary guidance for identifying when group replacement of LED signal modules is feasible is provided, and some possible avenues for future research are recommended.
