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Environmental Effects of Roadway Lighting on Ecosystems


Roadway lighting has been shown to measurably reduce fatal nighttime crashes. Yet roadway lighting can negatively impact insects and animals through attraction and disorientation or by disrupting their natural habitats. Transportation agencies are facing growing opposition to the use of nighttime lighting as a countermeasure to improve roadway safety. Local, state, and federal agencies, as well as members of the public are expressing a growing concern over consequences of nighttime lighting on the environment.

For example, the Federal Highway Administration, Federal Railroad Administration, and Federal Transit Administration in cooperation with the U.S. Fish and Wildlife Service have developed a programmatic consultation for transportation impacts to the endangered Indiana bat (Myotis sodalis) and the threatened Northern Long-Eared bat (Myotis septentrionalis). As a result of such actions, roadway lighting designers at DOTs across the country are beginning to encounter new challenges when planning routine lighting projects and are facing increasingly restrictive lighting regulations which in some cases threaten to subordinate what is considered good lighting practice used to provide enhanced driver safety.

While it is known that lighting has a negative impact on some species, it is not well understood whether those impacts can be minimized or otherwise mitigated by directional shielding, changing light levels or altering the spectral content of the light source. Therefore, there is a need to investigate the effects of artificial light to determine best practices which will allow designers to continue to provide essential lighting for safer roadways while minimizing its negative impacts. The expected results of this research will support at least four goals of the AASHTO Committee on Design. Specifically, they are Goal 2, Goal 4, Goal 5, and Goal 6. In addition, Goal 2 and Goal 3 of the Committee on Environment and Sustainability will be supported as well as Goal 2 of CES Natural Resources.


The Natural Sounds and Night Skies Division of the U.S. National Park Service (NPS) achieved International Dark Sky Park certification for Grand Canyon National Park and many other national parks in cooperation with the International Dark-Sky Association (https://www.nps.gov/subjects/nightskies/practices.htm). According to the NPS article, this was accomplished at Grand Canyon NP by converting a majority of existing fixtures within the park to a correlated color temperature (CCT) of 2,400K. The threshold of 3,000K or less seems to have become the de facto standard for safeguarding the environment from ALAN. However, current research is suggesting CCT in the range of 4,000K results in improved roadway safety through longer detection distances (NCHRP 05-22A).

CCT has often been used in conversation to characterize ALAN’s impact. However, CCT is better used to define appearance than impact. “Blue light” with a higher CCT value has been identified by some as bad lighting. The term “blue light” has been used in connection with LED fixtures since they have an increased short wavelength content in their spectrum compared to legacy light sources. Spectral content better defines the impacts to orientation, migration, reproduction, and other mechanisms within various species of light impacted organisms. Therefore, actinic spectrum (Longcore et al) shall be used, unless a more robust calculation method is available, to measure the potential impact of roadway lighting on the various species.

This research will serve as a beacon to inform the work of researchers currently working independently by bringing together both ecological and lighting team members to pioneer solutions. To make the scope of work more manageable, species that are impacted in similar ways by the more common spectrum, light levels, and designs of roadway lighting can be grouped together as needed. Where choices must be made to further limit the scope of this work, flora shall be considered subordinate to fauna.

This research will attempt to answer the following questions and make the following determinations;

1) Continue to expand and try to define a comprehensive list of species threatened by ALAN.

2) Determine the degree of endangerment for each species.

3) Determine whether dimming or part-night lighting will sufficiently mitigate or resolve the impacts on threatened ecosystems, while maintaining a safe visual environment for motorists.

4) Determine whether roadway luminaire style and orientation (limit the amount of uplight) will sufficiently mitigate or resolve the impact on various species.

5) Determine the spectral content (using commercially available LED fixtures) that sufficiently mitigates or eliminates environmental concerns, while maintaining a safe visual environment for motorists.

6) Develop a map so lighting designers across the country know exactly where ALAN is a concern. The map will provide a geographic model (like wind maps) with zones of influence for all species of concern.

7) Develop a point system, such as a scale of 1 to 10, that defines the relative importance of ecological safety for the various ALAN affected species. Provide this information as a map layer so it can be overlaid on the map defined in objective #6 above, thus allowing lighting designers to identify areas of greatest concern.

The information derived from spectral response once assigned to each species group will most likely offer a broad array of potentially conflicting solutions. In other words, the spectrum adjustments needed to mitigate impacts on one may be impossible or impractical to achieve in a normal roadway lighting application. Furthermore, what may resolve impacts for one specie may intensify the problem for other species. Therefore, the array of possible practical solutions will be identified along with a best fit solution or solutions for current roadway lighting practice which is based on current roadway lighting techniques and technology. Finally, this research shall develop a roadmap to detail any future research needs through which environmental impacts of roadway lighting are fully identified and addressed in order to eliminate adverse effects on ecosystems. For this research objective, a final report will be sufficient as the end product.


The urgency of this research has already been verified by the DOT representatives currently serving on the technical review panel for NCHRP 05-22A, Gaps and Emerging Technologies in the Application of Solid-State Roadway Lighting. Environmental impacts of roadway lighting have been identified as an emphasis area for that research work and this study will build upon NCHRP 05-22A.

Currently DOTs and municipalities around the country are rapidly converting legacy light sources to LED. The U.S. Department of Energy’s (DOE’s) Office of Efficiency and Renewable Energy estimates in their August 2020 report, Adoption of Light-Emitting Diodes in Common Lighting Applications that of the almost 50 million street and roadway lighting systems installed in the U.S. in 2018, almost half are now LED products. Furthermore, they estimate this is an increase of approximately 20% in just 2 years (since 2016). If these DOE estimates are accurate, then LED lighting will continue to replace legacy light sources on the nation’s interstate highways, roadways and streets at a staggering rate. This makes a better understanding of what is environmentally safe especially important and may help guide the deployment of outdoor LED fixtures throughout the country that are optimally tuned to the needs of the environment.

Related Research:

There is a growing body of literature documenting the negative impacts of artificial light at night (ALAN) on an ever-increasing list of species in both the plant and animal kingdoms. A search of ALAN on the National Institutes of Health’s PubMed.gov search engine through the United States National Library of Medicine’s National Center for Biotechnology Information brings up dozens or even hundreds of references and abstracts, depending on the key words used in the search. Many scholarly works now make it impossible to deny or ignore the direct relationship between ALAN and the negative consequences it has on the environment. A significant area of emphasis has developed around the study of ALAN’s influence on sleep, circadian rhythms, and human health.

At the same time, limited research is available on the impacts of roadway lighting on flora and fauna. Recently, street lighting was shown to have detrimental impacts on local insect populations (Boyes D, Evans D, Fox R, Parsons M, Pocock M, 2021). Typical roadway lighting levels were shown to create undesirable impacts on soybeans plants (Palmer, Gibbons, Bhagavathula, 2018). An article by Fraser, Collins, Longcore and Vickers (2020) summarizes literature regarding the effects of ALAN as well as traffic noise on animal behavior and occupancy. In an article which references various studies, the authors suggest ALAN is impinging on plant and animal behavior in regards to foraging, orientation, migration, seasonal reproduction, colonization and more (Falcón J, Torriglia A, Attia D, Viénot F, Gronfier C, Behar-Cohen F, Martinsons C, Hicks D, 2020). Another article describes ALAN’s impact on plant-pollinator interactions (Giavi S, Fontaine C, Knop E, 2021), while yet another article addresses the response of bat populations to ALAN (Seewagen CL, Adams AM, 2021). For many roadway lighting designers, this information is extremely disturbing and yet no clear guidance on how to mitigate these impacts is readily available to them in published lighting standards. While sufficient evidence exists to raise concern, there is still much to be understood about the mechanisms and ways to eliminate or reduce the effects of ALAN on the nighttime environment.


DOTs may use the proposed research results to update their roadway lighting design guidelines and guidelines for species impact evaluations. In addition, regulators, project managers, biologists and roadway lighting design engineers may use the research directly to support individual projects. The AASHTO Joint Technical Committee on Roadway Lighting will use the research results to consider making changes to the AASHTO Roadway Lighting Design Guide, which is referenced by many state DOTs and other agencies responsible for roadway lighting. Besides AASHTO, other national and international lighting organizations (such as the Illuminating Engineering Society, IES) may consider the report in future updates to their guidelines. Key AASHTO Committees and other organizations would likely be interested in the research results and could help support implementation: • AASHTO Joint Technical Committee on Roadway Lighting, Mark Luszcz, Chair, 302-760-2356, mark.luszcz@delaware.gov. • AASHTO Committee on Environment and Sustainability, Margaret Anderson-Kelliher, Minnesota DOT • Federal Highway Administration, Daniel Buford, 202-366-8168, daniel.buford@dot.gov • U.S. Fish and Wildlife Service, Catherine Liller, 303-236-4318, catherine_liller@fws.gov

Sponsoring Committee:AEP70, Environmental Analysis and Ecology
Research Period:12 - 24 months
Research Priority:High
RNS Developer:Mark Luszcz, DelDOT, Chair, AASHTO JTCRL, mark.luszcz@delaware.gov, (302) 760-2356 Kris Gade, Arizona DOT, Co-Chair, NRC for AASHTO CES. kgade@azdot.gov, (602) 292-0301 Mark Seppelt, Illinois DOT (retired), mark@wi-skies.com, (217) 691-9665
Date Posted:09/20/2021
Date Modified:10/19/2021
Index Terms:Environmental impacts, Street lighting, Ecosystems, Habitat (Ecology), Lighting systems,
Cosponsoring Committees: 

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