Evaluation of the Safety Performance of Continuous Mainline Roadway Lighting on Freeway Segments in Washington State

van Schalkwyk, Ida; Venkataraman, Narayan; Shankar, Venky; Milton, John; Bailey, Ted J.; Calais, Keith · 2016 · ROSA P / Washington (State). Dept. of Transportation. Office of Research and Library Services

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Summary

This study evaluates the safety performance of continuous mainline roadway lighting on freeway segments in Washington State, addressing the long-held assumption that such lighting significantly reduces nighttime crashes. The research was motivated by the Washington State Department of Transportation’s (WSDOT) need to optimize asset management, given the unsustainable growth of its lighting systems and a $5 million annual budget shortfall for replacements. With annualized life cycle costs reaching $13.5 million, WSDOT sought to determine if continuous lighting provided measurable safety benefits or if resources could be better allocated through illumination reform. The researchers conducted an extensive literature review of over 300 reports and critically evaluated common beliefs regarding lighting efficacy, identifying methodological flaws in prior studies, such as the inclusion of daytime crashes and failure to control for site-specific conditions. To generate new evidence, the team developed multivariate random parameter (RP) models using crash data from 2010 to 2014. Unlike previous studies that relied on simple nighttime-to-daytime crash rate ratios, this analysis strictly defined nighttime crashes as those occurring between the end of civil dusk twilight and the start of civil dawn twilight, using National Oceanic and Atmospheric Administration algorithms to ensure accurate classification. The models controlled for various roadway characteristics, including traffic volume, geometry, lane count, shoulder widths, and curvature, while categorizing lighting conditions as median continuous, right-side continuous, both-side continuous, point lighting, or no lighting. The results indicated that continuous illumination makes no measurable contribution to nighttime crash reduction on mainline freeway segments. The RP models demonstrated that the presence of continuous lighting did not correlate with improved safety performance when controlling for other variables. Consequently, the study concluded that installing continuous mainline lighting on freeways is not warranted for safety purposes. Additionally, a pilot project converting lighting to LEDs on US 101 showed that LED technology significantly increases energy efficiency and reduces greenhouse gas emissions while maintaining safety outcomes, further supporting the case for reform. Based on these findings, the authors recommend that WSDOT discontinue the requirement for continuous mainline lighting on freeways and consider removing existing lighting where segment-specific analysis indicates it is unnecessary. The study challenges traditional practices that rely on outdated crash modification factors and simplistic rate ratios, advocating instead for science-based, segment-specific evaluations. This shift aims to improve the sustainability of the transportation system, reduce environmental impacts, and optimize financial resources without compromising public safety.

Key finding

Continuous illumination makes no measurable contribution to nighttime safety performance on mainline freeway segments in Washington State.

Methodology

modeling

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified_with_issues.

Topics

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• roadway lighting effects
• visibility analysis litigation
• regulatory evaluation

Information type

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• Empirical Findings: crash risk outcomes