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Safety Impacts of Street Lighting at Isolated Rural Intersections – Part II
A consistently high percentage of rural intersection crashes occur at night in Minnesota and across the United States. The literature suggests that installing lighting at high-crash locations is a cost-effective measure to counter this problem. Several recent research efforts (including one initiated by the Minnesota Local Road Research Board) have supported this finding; however, many Minnesota highway agencies do not routinely install or maintain rural streetlights or use formal warrants or guidelines for their installation. The LRRB conducted a study, the objective of which was to evaluate the effectiveness of rural street lighting in reducing nighttime crashes at isolated rural intersections, so that Minnesota agencies have the information they need to make informed decisions about lighting installation.
Research Findings
Existing Mn/DOT lighting warrants currently limit the ability of agencies to implement street lighting at rural intersections – traffic signal volume warrants capture less than five percent of all rural intersections in Minnesota and the crash frequency warrant captures less than two percent. This finding is critical in light of the research findings.
The results of the investigation of safety impacts of street lighting at isolated rural intersections suggested that the installation of street lighting may contribute to the reduction in the frequency of crashes (night to total crash ratio) and nighttime crash rates. This finding was consistent with the findings of a previous LRRB study and provides Mn/DOT with confidence that lighting is another safety countermeasure tool to reduce the number crashes at rural Minnesota intersections.
Recommendations
In order to effectively implement street lighting as a safety tool at rural intersections for all Minnesota agencies, it is recommended that Mn/DOT modify the current lighting warrants in the Traffic Engineering Manual and any subsequent documents with reference to installation of lighting on Minnesota’s roadways. Modified volume warrants should apply to a higher percentage of Minnesota rural intersections and provide quantifiable volume and crash measurements, as well as a consideration of roadway functional classification. These changes would give Mn/DOT and other agencies the authority to implement street lighting as a safety measure based on revised warrants and guidelines.
Modified lighting warrants would allow Minnesota agencies to implement lighting as a safety measure as either a proactive or reactive approach. Agencies may choose to install lighting due to high crash experiences or install lighting at an intersection based on functional classification and volumes on both the major and minor approaches.
The full report is available at http://www.lrrb.org/pdf/200635.pdf. For those interested in reading Part I of this research investigation, this report is also available online at http://www.lrrb.org/pdf/199917.pdf
For more information, contact Roger Gustafson, Carver County Engineer, at rgustafson@co.carver.mn.us or 952.466.5200.
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