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Suggested Citation:"Chapter 1. Introduction." National Academies of Sciences, Engineering, and Medicine. 2020. Solid-State Roadway Lighting Design Guide: Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/25679.
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Page 8
Page 9
Suggested Citation:"Chapter 1. Introduction." National Academies of Sciences, Engineering, and Medicine. 2020. Solid-State Roadway Lighting Design Guide: Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/25679.
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Page 9
Page 10
Suggested Citation:"Chapter 1. Introduction." National Academies of Sciences, Engineering, and Medicine. 2020. Solid-State Roadway Lighting Design Guide: Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/25679.
×
Page 10
Page 11
Suggested Citation:"Chapter 1. Introduction." National Academies of Sciences, Engineering, and Medicine. 2020. Solid-State Roadway Lighting Design Guide: Volume 2: Research Overview. Washington, DC: The National Academies Press. doi: 10.17226/25679.
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Page 11

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1 CHAPTER 1. INTRODUCTION REPORT OVERVIEW AND ORGANIZATION This report constitutes the Draft Final Report for the National Cooperative Highway Research Program (NCHRP) Project 05-22 Guidelines for Solid State Lighting. The report is organized as follows: • Chapter 1 provides an overview of the project, its intended objectives, and the research methodology used to produce the research results. • Chapter 2 provides a summary of the current state of Solid State Lighting (SSL) adoption and specifications and guidance documents developed by state agencies to date. • Chapter 3 describes the structure for the SSL Guide. This structure mirrors the structure of the American Association of State Highway and Transportation Officials (AASHTO) Roadway Lighting Design Guide, to the extent possible, to facilitate any future integration of the two documents. • Chapter 4 provides a literature review of relevant research associated with the application of SSL and includes a gap analysis of items needed for this project and future research. • Chapter 5 describes the research performed as part of this project. The results of this research are included in the SSL Guide and outstanding questions are included in the Research Roadmap section of this report. RESEARCH OBJECTIVES The objectives of this report are to determine the current guidance for the use of SSL, identify the research that still needs to be accomplished to assist in its proper implementation, and develop a comprehensive, easy to use, set of guidelines using currently available information and new research being proposed as part of this project. These guidelines address required light levels, effects of spectral characteristics, light level options for use with adaptive lighting, a design approach (including areas of the roadway and shoulders that may require lighting), electrical considerations, control methodologies, asset management approaches, methodologies to minimize any potential environmental or health effects, and information about SSL design methodologies that may be included in the AASHTO Roadway Lighting Design Guide, State Department of Transportation (DOT) manuals, standard specifications, and standard drawings.

2 KEY FINDINGS The literature review and testing on the Smart Road support several key findings that are incorporated into the SSL Guide. These include: 1. Providing light beyond the limits of the roadway travel lanes benefits drivers’ visual performance. Using a certain amount of light (called the surround ratio) in shoulder areas adjacent to the roadway increased a driver’s visual performance. Increasing the surround ratio also increased the visual performance of drivers of all age groups at both tested speeds. 2. Spectral content of light-emitting diode (LED) sources should be a design consideration. While, under most conditions, no major differences were observed between the correlated color temperatures of LED light sources or between the LED and High-Pressure Sodium (HPS) light sources in terms of driver visual performance, visual performance under 4000K LED was the highest at both the tested speeds and higher surround ratios. 3. Discomfort glare ratings were mainly affected by the light levels, and even at the highest light level evaluated, they were lower than “noticeable.” None of the evaluated light sources (LEDs of all Correlated Color Temperature [CCTs] and HPS) were a significant source of discomfort glare. 4. Methodologies for designing adaptive lighting systems are available and are included in the SSL Guide. 5. Electrical considerations are different for SSL sources, and recommendations for design are included in the SSL Guide. 6. Maintenance and light loss considerations are different for SSL sources and are outlined in the SSL Guide. 7. Research does not currently show any health impacts from properly designed roadway lighting.

3 RESEARCH APPROACH SSL has several key differences from the currently widely used High Intensity Discharge (HID) products and more specifically from HPS sources. These areas include: • Spectral content: The broader spectral content of SSL products can have an impact on visibility, perceived brightness, and other physiological responses. • Optical control and distribution: SSL sources offer greater flexibility in designing custom optical distributions from luminaires. As a result, additional factors like off-roadway illumination, light trespass, roadway versus shoulder lighting, uniformity, and other factors can be considered and controlled. • Output control and monitoring: The ability of SSL sources to be dimmed and monitored offer opportunities in adaptive lighting control, integration with asset management systems, and coordination with SMART city or Intelligent Transportation System (ITS) systems. Current AASHTO design recommendations do not highlight these differences as a part of the design guide. This research addresses as many of these factors as possible within the constraints of this project. Future research will be identified and included in the Research Roadmap for that are not addressed with this research. Figure 1 presents the overall workflow of the project. Figure 1. Overview of the NCHRP Project 05-22 Workflow Data • Survey of DOTs and Industry • Collection of Specifications / Current Practices Work Plan • Identify Research that can Currently be Implemented • Identify Available Best Practice • Identify Needed Reseach • Develop Contents for Guidelines and Roadmap Implementation • Guideline Document and Standard Specification for DOT use of SSL • Roadmap and Potential Funding Sources for Needed Research

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Providing light beyond the limits of the roadway travel lanes benefits drivers’ visual performance, spectral content of light-emitting diode (LED) sources should be a design consideration, and there are not currently any health impacts from properly designed roadway lighting are among the findings of this survey report.

The TRB National Cooperative Highway Research Program's pre-publication draft of NCHRP Research Report 940: Solid-State Roadway Lighting Design Guide: Volume 2: Research Overview determines the current guidance for the use of Solid State Lighting (SSL); identifies the research that still needs to be accomplished to assist in its proper implementation; and develops a comprehensive, easy to use, set of guidelines using currently available information and new research being proposed as part of this project.

Also see this guide's accompanying pre-publication draft, NCHRP Research Report 940: Solid-State Roadway Lighting Design Guide: Volume 1: Guidance.

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