The lighting industry has changed dramatically over the past decade. The optics of legacy high intensity discharge (HID), full-cutoff luminaires were restricted to the lamp and reflector design; these lamps emit light in almost every direction, which must then be reflected to the roadway. Roadway luminaires have moved beyond this design through the vast possibilities presented by solid-state lighting (SSL)—at present, in the form of light emitting diodes (LED)--which also boasts lower energy usage, reduced maintenance, and improved color. AASHTO target light levels are calculated over a grid limited to the traveled roadway. Any light that lands outside of the calculation grid is not quantified in the average and uniformity results, but is still present with roadway luminaires and may provide a safety benefit. With the greater ability to control the distribution and the sharp cutoff at the edges with SSL luminaires, light levels beyond the calculation grid may be dramatically reduced, but a design may still meet the AASHTO criteria. Therefore, research is needed to investigate the application of AASHTO criteria to SSL roadway lighting and, if the results dictate, provide guidance for light level criteria for areas immediately adjacent to the traveled roadway when using SSL luminaires. Additional research is also needed to explore the benefits and challenges of adaptive lighting and provide further guidelines for its use, as well as the environmental and health effects of roadway lighting.
The objectives of this project were to develop more comprehensive guidelines in AASHTO standard format for the application of roadway lighting related to the widespread adoption of SSL, and to identify gaps in knowledge where possible future research will enhance these guidelines. The research shall complement and supplement the ongoing efforts of the AASHTO Roadway Lighting Committee on the usage of SSL lighting.
STATUS: The guide and final report are available here as NCHRP Report 940, Volume 1 and Volume 2.