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NCHRP Web-Only Document 146: Replacement Processes for Light Emitting Diode (LED) Traffic Signals 2 CHAPTER 2 RESEARCH APPROACH The project activities, documented in the present report, consisted of the following: ⢠A review and synthesis of recent human factors research relevant to the visibility and photometric performance of LED traffic signals. ⢠Evaluation of methods for laboratory and field measurement of LED traffic signal photometric performance. ⢠Investigation of failure modes of LED traffic signal modules. ⢠Summary of considerations for departments of transportation (DOTs) in specifying, deploying and maintaining LED traffic signals. The results of the aforementioned tasks are documented in Chapter 3 of this report, "Findings and Applications." Chapter 4, "Conclusions, Recommendations, and Suggested Research," provides some preliminary guidelines for DOTs regarding practices for maintenance and replacement of LED traffic signal heads.
