Environmental Effects of Roadway Lighting on Wildlife

Focus Area

Wildlife & Ecosystems


Natural Resources






2-3 years

Research Idea Scope

Roadway lighting has been shown to measurably reduce nighttime fatal and other crashes. However, roadway lighting can negatively impact insects and animals through attraction and disorientation or by disrupting their natural habitats. Artificial nighttime lighting is thought to reduce occupancy of habitat areas adjacent to roadways for some species and may decrease use of wildlife crossing structures. Additionally, nighttime lighting attracts insects and may indirectly lead to increased road mortality for bats and other insectivorous animals.
Transportation agencies are facing growing opposition to the use of nighttime lighting as a countermeasure to improve roadway safety from members of the public concerned with potential consequences of nighttime lighting on the surrounding environment. 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 the type/color of the light source. Therefore, there is a need to investigate the effects of artificial light on wildlife to determine best practices to provide lighting to support driver safety while minimizing negative impacts to surrounding ecosystems.
The expected results of this research will include new information regarding roadway lighting that will allow this important crash countermeasure to be implemented while minimizing impacts on wildlife.

Literature Search Summary
There is some research available on the impacts of roadway lighting on flora. For instance, the effects of roadway lighting on soybeans was studied in Illinois which proved that typical roadway lighting levels will adversely impact this important cash crop unless trespass light is managed properly (Palmer, Gibbons, Bhagavathula, 2018). A recent article by Fraser, Collins, Longcore and Vickers (2020) summarizes literature regarding the effects of artificial nighttime light as well as traffic noise on animal behavior and occupancy. Lighting was also addressed in a chapter in the Handbook of Road Ecology (2015, van der Ree, Smith and Grilo, Eds.). However, there is much to be understood about the mechanisms and ways to minimize or mitigate effects of artificial nighttime lighting on wildlife.

Research Objective
The objective of this research is to develop roadway lighting recommendations that can minimize negative impacts on wildlife species that are sensitive to artificial lighting. The research should consider the scope and magnitude by which outdoor lighting in general and roadway lighting more specifically influences species of animals in an adverse manner (i.e., sea turtles, reduced roadway crossings or use of wildlife structures) and propose solutions to mitigate these impacts. This roadmap will also serve to inform the work of researchers currently working independently by bringing together both ecological and lighting team members to pioneer solutions.
Task 1 will identify groups of wildlife species that are impacted in similar ways by the more common spectrum, light levels, and designs of roadway lighting and evaluate the direct impacts, both positive and negative, to each of these groups. Then suggestions for design and management practices to reduce impacts for each group or impact type will be developed.
Task 2 will examine the impacts of different light spectrums to particular groups of species identified in Task 1. Correlated color temperature (CCT) has been often used in conversation to characterize this impact but CCT is a better metric to define appearance not spectral impact. 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 of fauna.
The information derived from spectral response once assigned to each species group will 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 may intensify the problem for another 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.
Task 3 will be to develop a research roadmap to detail the future research needs through which environmental impacts of roadway lighting are fully identified and addressed in order to eliminate adverse effects on wildlife. For this research, a final report will be sufficient as the end product. AASHTO and other national and international lighting organizations (such as the Illuminating Engineering Society, IES) may consider the report in future updates to their guidelines.
Problem Statement Author(s)
Mark Seppelt, formerly Illinois DOT, [email protected]
Mark Luszcz, DelDOT, Chair, AASHTO Joint Technical Committee on Roadway Lighting, [email protected]
Kris Gade, Arizona DOT, Co-Chair, Natural Resources Committee for AASHTO CES, [email protected]

Urgency and Payoff

The magnitude of potential impact must be determined before incorrect lighting designs are deployed in a nonrecoverable fashion. Currently DOTs around the country are converting high pressure sodium (HPS) luminaires to light emitting diode (LED) roadway fixtures as HPS is no longer supported by most fixture manufacturers. The correlated color temperature differs between these two light sources and can differ among LED luminaires depending on which LED is selected. Likewise, the spectrum can vary in blue light content depending on the specific LED fixture selected.
A proper understanding of the impacts of LED roadway lighting on fauna can prevent a large deployment of fixtures throughout the country that are not optimally tuned to the needs of the environment. In addition, recommendations for adjusting lighting design at wildlife crossing locations may increase the use of these structures as well.
This research would be considered by the entity within each DOT responsible for the DOT’s roadway lighting design guidelines, as well as individual roadway lighting design engineers. The information would also be useful to DOT biologists and landscape architects for evaluating impacts of lighting on wildlife and designing pedestrian-oriented areas to be more wildlife friendly.
DOTs may use the proposed research results to update their roadway lighting design guidelines and guidelines for species impact evaluations. In addition, individual 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. The AASHTO Committee on Environment and Sustainability will disseminate the results to state DOT biologists to guide suggestions for reducing impacts of lighting on wildlife.
The IES may also use the results of this research to update their guidelines. Webinars and trainings would also be useful for environmental planners and biologists at DOTs to better understand the impacts of different types of lighting designs and possible approaches to mitigation.

Suggested By

Mark Luszcz

[email protected]