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1 Report Overview and Organization This volume constitutes the final report for National Cooperative Highway Research Pro- gram (NCHRP) Project 05-22, âGuidelines for Solid-State Roadway Lighting.â The report is organized as follows: â¢ Chapter 1 provides an overview of the project, its intended objectives, and the research meth- odology used to produce the research results. â¢ Chapter 2 provides a summary of the current state of solid-state lighting (SSL) adoption and specifications and the guidance documents developed by state agencies to date. â¢ Chapter 3 describes the structure of NCHRP Research Report 940: Solid-State Roadway Light- ing Design, Volume 1: Guidance (SSL Guide). To the extent possible, this structure mirrors that of the AASHTO Roadway Lighting Design Guide (AASHTO 2018b), so as to facilitate any future integration of the two documents. â¢ 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. â¢ 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 discussed in âResearch Road- mapâ in Chapter 5. Research Objectives The objectives of this report are to determine 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 that draws on 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 mini- mize potential environmental or health effects, and information about SSL design methodolo- gies that may be included in the AASHTO Roadway Lighting Design Guide, state department of transportation (DOT) manuals, standard specifications, and standard drawings. Key Findings The literature review conducted for this project and the results of testing on the Virginia Smart Road support several key findings that are incorporated into the SSL Guide: 1. Providing light beyond the limits of the roadway travel lanes benefits driversâ visual per- formance. Using a certain amount of light (called the surround ratio) in shoulder areas C H A P T E R 1 Introduction
2 Solid-State Roadway Lighting Design adjacent to the roadway increases a driverâs visual performance. Increasing the surround ratio also increases the visual performance of drivers of all age groups (this was found at both tested speeds). 2. Spectral content of light-emitting diode (LED) sources should be a design consideration. Although, under most conditions, no major differences were observed between the correlated color temperatures (CCTs) of LED light sources or between 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 the higher surround ratios. 3. Discomfort glare ratings were mainly affected by light levels, and even at the highest light level evaluated, they were lower than ânoticeable.â None of the evaluated light sources (LEDs of all CCTs and HPSs) was 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. Research Approach SSL has several key differences from the high-intensity discharge (HID) products that currently are widely used and, more specifically, from HPS sources. These differences include the following: â¢ Spectral content: The broader spectral content of SSL products can have an impact on visibility, perceived brightness, and other physiological responses. â¢ Optical control and distribution: SSL sources offer greater flexibility in designing custom optical distributions from luminaires. As a result, additional factors such as off-roadway illumination, light trespass, roadway versus shoulder lighting, uniformity, and other factors can be considered and controlled. â¢ Output control and monitoring: The ability of SSL sources to be dimmed and monitored offers 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. The research reported here addresses as many of these factors as possible within the constraints of this project. For topics that are not addressed with this research, future research is identified in âResearch Roadmapâ in Chapter 5. Figure 1 presents the overall workflow of the project.
Introduction 3 Data â¢ Survey of DOTs and industry â¢ Collection of specifications/current practices Work Plan â¢ Identify research that can currently be implemented. â¢ Identify available best practices. â¢ Identify needed reseach. â¢ Develop contents for guidelines and roadmap. Implementation â¢ Guidance document and standard specification for DOT use of SSL â¢ Roadmap and potential funding sources for needed research Figure 1. Overview of workflow for NCHRP Project 05-22.