Document Type

Technical Report

Publication Date



Traffic safety -- Oregon, Oregon. Department of Transportation, Roads -- Lighting -- Effects on traffic safety


In 2001, Oregon’s governor responded to a perceived future energy shortage in the Pacific Northwest by directing all state agencies to reduce power consumption by 10 percent. After review of power saving opportunities, the Oregon Department of Transportation (ODOT) elected to include selective illumination reductions on Oregon interstate highways as part of their energy saving strategy. The illumination reductions occurred at interchanges and along lineal highway sections between October 2001 and April 2002. A total of 47 interchanges and 6.03 miles of interstate highways were modified. Changes in illumination were broadly classified as either full (including high-mast) to partial designs, partial plus to partial designs, or lineal reductions. In this study, no before or after field measurements were taken of actual luminance values, lighting coverage, or other design specific values. This research evaluated the changes in safety performance using crash, geometry, weather and volume data from years 1996 to 2005 using observational before-after evaluations using the : 1) the simple before-after and 2) empirical-bayes approach. The empirical-bayes approach found a 3.47 percent increase (4.65 standard deviation) in total night crashes where full interchange lighting was reduced to partial lighting. Fatal and injury night crashes, however, were found to decrease by 11.38%. For interchanges where illumination was reduced from partial plus to partial, a 35.24 percent decrease in total night crashes was found. A 29 percent increase in total night crashes (18.21 standard deviation) on sections where the lineal lighting was modified was found. Weighing all evidence, the research concludes that a decrease in safety performance occurred on the lineal freeway sections and at full to partial design locations. An observed decrease in safety performance was not found at the partial plus to partial lighting design modifications.


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