National Academies Press: OpenBook

Solid-State Roadway Lighting Design Guide: Volume 1: Guidance (2020)

Chapter: Chapter 6 - Roundabouts, Interchanges, and Intersections

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Page 36
Suggested Citation:"Chapter 6 - Roundabouts, Interchanges, and Intersections." National Academies of Sciences, Engineering, and Medicine. 2020. Solid-State Roadway Lighting Design Guide: Volume 1: Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25678.
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Page 36

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

36 Roundabouts, Interchanges, and Intersections Current Guide The current AASHTO Roadway Lighting Design Guide (AASHTO 2018) discusses the lighting of roundabouts, pole placement, and the extent of the lighting system. It recommends 1.3 to 2 times the lighting level of the highest illuminated approach road and extending the light levels 6 to 10 ft (1.8 to 3.0 m) outside the outer curb to the sidewalk or other roadside features. This chapter in the guide does not address intersections and interchanges, which are included in Chapter 3 of the current AASHTO guide. Complete interchange lighting is designed to the same levels as the roadway, but no light level requirements are given for partial interchange lighting. Light levels for intersections are recommended to be equal to the sum of the two intersecting roadways. The guide also includes recommendations for crosswalk lighting at intersections where vertical lighting levels along the centerline of the crosswalk at 5 ft (1.5 m) in height would be equal to the horizontal levels being provided. Additional Considerations When Using LED Sources Existing AASHTO recommendations would not change for LED sources. Meeting the AASHTO recommendation of lighting 6 to 10 ft (1.8 to 3.0 m) outside the outer curb would provide enough surround lighting, which can sometimes be limited with LED optical systems. Additional considerations for LED luminaires include • Use of 4000K CCT sources to assist in the detection distance for pedestrians and hazards at these facilities, • Levels for adaptive lighting at the facilities that vary with the approach roads, and • Vertical lighting levels in crosswalks at roundabouts that meet the same requirements as crosswalks at intersections. Key Issues for Roundabouts, Interchanges, and Intersections • Consider 4000K CCT sources for roundabouts, interchanges, and intersections. • Consider vertical lighting requirements in all crosswalk locations. C H A P T E R 6

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The lighting industry has changed dramatically over the past decade. The optical system design of legacy high-intensity discharge (HID) luminaires was restricted to the lamp, refractor, and reflector design, which had limits in the distribution of the light, controls, and adaptability. Roadway luminaires have moved beyond this design methodology to include the vast possibilities presented by solid-state lighting (SSL). At present, in the form of light emitting diodes (LED), SSL uses lower energy, reduces maintenance, improves color, and can be easily dimmed and controlled.

The TRB National Cooperative Highway Research Program's NCHRP Research Report 940: Solid-State Roadway Lighting Design Guide: Volume 1: Guidance develops more comprehensive guidelines in American Association of State Highway Transportation Officials (AASHTO)-standard format for the application of roadway lighting related to the widespread adoption of SSL, and identifies gaps in knowledge where possible future research will enhance these guidelines.

Also see this guide's accompanying report, NCHRP Research Report 940: Solid-State Roadway Lighting Design Guide: Volume 2: Research Overview.

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