The National Academies

NCHRP 05-25 [Anticipated]

Safety Performance of LED and Variable Lighting Systems

  Project Data
Source: AASHTO Committee on Safety
Funds: $650,000
Staff Responsibility: Jennifer L. Weeks
Fiscal Year: 2021

This project has been tentatively selected and a project statement (request for proposals) is expected in August 2020. The project statement will be available on this site. The problem statement below will be the starting point for a panel of experts to develop the project statement.

Safety is a paramount issue for motorized and non-motorized road users. In an era that sees increasing challenges with keeping up with the life-cycle costs of added infrastructure, including lighting hardware and electrical systems, the ability to optimize where, when, and how much lighting to place throughout the system is critical. While roadway lighting is a common countermeasure used to increase visibility at night and it is recognized that lighting may offer substantial safety benefits, not all locations will experience benefits to the same extent because of the localized characteristics, climate, and circumstance. In addition, the environmental impacts (e.g., on animals, plants, and energy consumption) further create urgency to better understand safety performance as part of countermeasure selection and asset management so that a more thorough understanding of trade-offs can be gained. The need to light for vehicles may differ greatly than those for vulnerable road users, but choosing one mode’s needs over the other may not lead to optimal solutions that balance the safety needs with environmental and asset management concerns. With the advent of LED and adaptive roadway lighting systems, the lighting characteristics can be adjusted as a function of need that may increase safety performance at a much lower cost and save energy. Adaptive lighting also allows for adjustment of roadway lighting levels based on real-time data. Reducing lighting levels at night when traffic volumes are low has been shown to not adversely affect safety performance. However, much of the criteria for determining when and how to adjust systems are limited and based on older research using less statistically reliable methods.

The objective of this research is to develop safety performance models that will evaluate the impacts of LED and variable lighting systems in different roadway contexts, conditions, and for different user groups. This research would include a critical scientific review of the current state of the practice related to lighting design in different contexts, the scientific basis for the lighting design decisions and warrants, the assumptions regarding the safety benefits for these installations, under what conditions, and the level of scientific rigor applied to estimates in manuals used by practitioners. The project would evaluate the trade-offs related to lighting systems under different conditions and operating scenarios and investigate the safety effects of roadway lighting through random coefficient models or similar models to allow for crash effects to be considered as a distribution versus fixed coefficients along with cross section and contextual characteristics to allow for analyzing roadway, roadside, traffic, and weather characteristics impact on the safety performance of the lighting. The research will use and add to the data sets used for the development of Chapters 18 and 19 in the Highway Safety Manual (HSM 1st Edition), and incorporate existing knowledge regarding relationships between cross section, geometrics, and other factors to safety performance into guidelines for the installation of lighting and variable lighting systems.

The deliverables will enable agencies to determine when it may be appropriate for additional or less lighting through removal of unneeded lighting or installation of new adaptive lighting and what protocols agencies should follow for each of these scenarios on limited access freeways and multilane roadways. Results of this research could be included in the Highway Safety Manual, Crash Modification Clearinghouse, and AASHTO and FHWA lighting design guidelines roadway design manuals. Individual states may also incorporate the research results in their policies and manuals.

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