Study Details

Study Title: Effect of Roadway Lighting on Safety

Authors: Runyan et al.

Publication Date: SEP, 2024

Abstract: A significant portion of severe crashes and severe crashes involving vulnerable road users (VRU), 29 percent and 39 percent respectively, occur at night in Utah. Nighttime crash causes are less understood than daytime crashes as there are fewer nighttime crashes, but it is generally assumed that increasing street lighting can help mitigate these crashes. To test this assumption, the Utah Department of Transportation (UDOT) was interested in developing Crash Modification Factors (CMFs) specific to the state of Utah which correlate the quantity and quality of light to crash outcomes, to observe how specific light quantities and qualities might reduce nighttime crashes. Average illuminance and light uniformity metrics were measured for several arterial roads in Utah and statistical models were used to build models for estimating CMFs. CMFs indicated that average illuminance was not correlated to a significant change in crashes except when increasing illuminance above 0.3 foot-candles (fc). This indicates that some light is better than none, but the benefit of increasing existing light levels may not be significant. However, CMFs for the uniformity of light indicated that less uniformity correlated to fewer crashes at lower average illuminance, and more crashes at higher illuminance. This may show that it is more important to light specific locations than to light entire road segments evenly, unless light levels are already high. Despite the possible benefit of increasing uniformity on roadways with high light levels, most uniformity CMFs suggested that future research should be focused on locations like crosswalks where lighting is most important.

Study Citation: Runyan, S., D. Bassett, G. Schultz, B. Brimley, G. Snow, A. Simpson and B. Dahl. "Effect of Roadway Lighting on Safety" Report No. UT-24.12. Utah Department of Transportation. Salt Lake City, Utah. (September 2024).

Study Report: Download the Study Report Document


CMFs Associated With This Study

Category: Highway lighting

Countermeasure: Improve street lighting illuminance and uniformity

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.9913 StarsAllAllNot specifiedUrban
0.9463 StarsAllAllNot specifiedUrban
0.73274 StarsAllAllNot specifiedUrban
0.81193 StarsAllAllNot specifiedUrban
0.85153 StarsAllAllNot specifiedUrban
0.82184 StarsAllAllNot specifiedUrban
0.86143 StarsAllAllNot specifiedUrban