Researchers link visibility and safety from roadway lighting

February 05, 2013

UNIVERSITY PARK, Pa. — Driving at night is no picnic and can be fraught with danger, given the sometimes severe visibility limits and scarce reaction time. While roadway lighting can improve visibility at night and give drivers more response time to potential hazards, relating visibility from roadway lighting to nighttime driving safety has been limited by a shortage of data and lack of consideration of vehicle headlights.

To address this issue, Eric Donnell, associate professor at Penn State and faculty researcher at the University's Thomas D. Larson Pennsylvania Transportation Institute, in collaboration with researchers at the Rensselaer Polytechnic Institute's Lighting Research Center, developed a unique parallel approach to lighting safety analysis.

The team used lighting and crash data for state highway intersections in Minnesota to develop quantitative models relating nighttime driving safety to the presence of lighting at these intersections. The models also accounted for the effects of features like signals, medians and other intersection design and operational features in order to segregate the effects of lighting from these other aspects. Various statistical approaches were applied to confirm the results. Data for the statistical analyses were provided by the Minnesota Department of Transportation through the Federal Highway Administration's Highway Safety Information System.

The researchers also modeled prototypical roadway intersections with and without lighting, including the effects of vehicle headlights. In doing so, they were able to estimate drivers' ability to detect potential hazards quickly and accurately under each lighting scenario compared to when no roadway lighting was present.

"A lot of research has been done on driver safety and roadway lighting," said Donnell. "What's noteworthy here is the connection between the visibility and traffic safety research methods, which made it possible to link them with empirical data."

Donnell collaborated with Mark Rea, Lighting Research Center director and professor, and John Bullough, the center's senior research scientist.

"While the finding that safety benefits from roadway lighting are highly related to the visibility improvements lighting provides is not novel nor unexpected, evidence for this direct link has been scarce in the literature," said Rea. "Our models provide a tool that transportation agencies can begin using now to not only allocate lighting more efficiently, but to design lighting more effectively."

As new practices such as solid-state lighting, adaptive roadway and vehicle lighting, and benefit-cost analysis continue to emerge, tools like those described by Donnell, Rea and Bullough will help agencies specify and shape lighting that minimizes energy use and environmental impact while maximizing the use of limited public resources.

The full text of the paper, titled "To illuminate or not to illuminate: Roadway lighting as it affects traffic safety at intersections," is available at

  • IMAGE: Annemarie Mountz

(Media Contacts)

Last Updated February 06, 2013