Title

Safety effects of reducing freeway illumination for energy conservation

Document Type

Article

Publication Date

September 2008

Abstract

The addition of illumination where none was present is generally believed to have a positive effect on motor vehicle safety; reducing the frequency, as well as the severity of crashes. The operational cost of illumination, however, can make it a candidate for conservation during periods of high energy costs. In response to a forecasted energy shortage, the Oregon Department of Transportation selectively reduced illumination on interstate highways as part of an energy-saving effort. The reductions occurred at 44 interchanges and along 5.5 miles of interstate highway. This paper presents the results of a crash-based analysis of the changes in safety performance using an empirical-Bayes observational methodology. The study found an increase in reported crashes where the lineal lighting was reduced both in total crashes (28.95%, P = 0.05) and injury night crashes (39.21%, P = 0.07). Where full interchange lighting was reduced to partial lighting, a 2.46% increase (P = 0.007) in total night crashes was observed. Injury night crashes, however, decreased by 12.16% (P < 0.001) though day injury crashes also decreased at these locations. Unexpectedly, for interchanges where illumination was reduced from partial plus to partial, a 35.24% decrease (P < 0.001) in total crashes and 39.98 (P < 0.001) decrease in injury night crashes was found, though again, day crashes also decreased.