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

015988052016Research Report: January 2013-March 2016PDFTech ReportWA-RD 855.1Street lightingSafetyNighttime accidentsLight emitting diodesFreewaysEnvironmental impactsRecommendationsDesignHighwaysSafety and Human FactorsEnergy efficienceSafety performanceNighttime crashesRoadway lightingLED conversionSafety performance of roadway lightingIlluminationUnited StatesWashingtonWashington (State). Dept. of Transportation. Office of Research and Library Servicesvan Schalkwyk, IdaVenkataraman, NarayanShankar, VenkyMilton, JohnBailey, Ted J.Calais, KeithWashington (State). Department of TransportationPennsylvania State University. Department of Civil and Environmental EngineeringWashington (State). Dept. of Transportation. Research OfficeUnited States. Federal Highway AdministrationUS Transportation CollectionWashington State Department of Transportation (WSDOT) evaluated continuous roadway lighting on mainline freeway segments in Washington State. An extensive literature review on the safety performance of roadway lighting was completed. As part of this research effort WSDOT developed multivariate random parameter (RP) models with specific lighting variables for continuous lighting on mainline freeway segments. Roadway lighting is often used as a countermeasure to address nighttime crashes and this research evaluates common assumption related to roadway lighting. The models developed for this research use crashes from the end of civil dusk twilight to the start of civil dawn twilight since lighting systems are of limited value outside these timeframes. Natural light conditions were estimated for crashes based on location and time of the crash event. Based on the RP results, the research team concludes that the contribution of continuous illumination to nighttime crash reduction is negligible. In addition to the findings on safety performance, a pilot LED project on US101 demonstrated that LED roadway lighting can significantly increase energy efficiency and environmental stewardship (e.g., reducing greenhouse gas emissions) while maintaining safety performance outcomes. The research team recommended modification to WSDOT design policy, including removal of the requirement of continuous mainline lighting and reduction of lighting where segment specific analysis indicates appropriate