Lighting

Roadway lighting provides greater intersection visibility of the intersection, signs, and markings.

Description

Intersection crashes during nighttime hours may occur due to drivers being unable to see conflicting traffic or because the driver is unaware of the intersection until it is too late to avoid a collision. In rural areas, typically the only source of lighting is provided by vehicle headlights. Roadway lighting provides greater intersection visibility of the intersection, signs, and markings (Atkinson et al. 2014 and Neuman et al. 2003). Even when only a single light is used, lighting may also indicate an upcoming intersection and alert drivers to changing roadway conditions.

Placement

Lighting is best for intersections with a high number of nighttime crashes. In particular, rear-end, right angle, and turning crashes may suggest that drivers are unaware of the intersection (Atkinson et al. 2014). As noted by Neuman et al. (2003), the keys to successful application of lighting are to identify sites where lack of lighting is a significant contributing factor to nighttime crashes and to develop an appropriate lighting system using AASHTO and the Illuminating Engineering Society of North America criteria.

Chapter 6 of the Iowa DOT Traffic and Safety Manual discusses warrants for lighting (Iowa DOT 2014) and Chapter 11 of the Iowa Statewide Urban Design Standards (SUDAS 2014).

Effectiveness

A study in Iowa showed that the mean number of nighttime crashes at intersections with no lighting is two times higher than locations where lighting is present (Isebrands et al. 2010).

As noted in the table below, a number of studies have been conducted that show the benefits of lighting at rural unsignalized intersections.

Author (R)ural
(U)rban
Study Location Sample Size Change in Nighttime Crashes
Carstens and Berns 1984 R IA 91 none
Roberts and Walker 1976 R IA 47 -49%
Isebrands et al. 2010 R MN 33 -37%
Green et al. 2003 R/U KY 9 -45%
Preston and Schoenecker 1999 R MN 12 -25% to -40%
Wortman and Lipinski 1972 R IL N/A -30%

Advantages

  • Shown to be effective in multiple studies
  • Can be installed in a reasonable time frame

Disadvantages

  • Requires power source which may be problematic in remote rural areas
  • Cost

Additional information is provided in this technical brief.

Iowa-Specific Resources

Strategies to Address Nighttime Crashes at Rural, Unsignalized Intersections
Summarizes countermeasures to address nighttime crashes at rural intersections, summarizes lighting. warrants and practices used by other states, and summarizes lighting warrants and practices used by other states.

References

Atkinson, Jennifer E., Brian E. Chandler, Vernon Betkey, Karen Weiss, Karen Dixon, Anna Giragosian, Kelly Donoughe, and Cara O'Donnell. Manual for Selecting Safety Improvements on High Risk Rural Roads. Report FHWA-SA-14-075. Federal Highway Administration, 2014.

Carstens, R. L. and L. D. Berns. Roadway Lighting on Secondary Roads in Iowa. Iowa Department of Transportation, 1984.

Green, Eric R., Kenneth R. Agent, Monica L. Barrett, and Jerry G. Pigman. Roadway Lighting and Driver Safety. Report KTC-03-12/SPR247-02-IF. Kentucky Transportation Center, University of Kentucky, 2003.

Iowa DOT. "Chapter 6: Lighting. Iowa DOT." Iowa DOT Traffic and Safety Manual. Iowa DOT, Office of Traffic and Safety, 2014.

Isebrands, Hillary, Shauna Hallmark, Wen Li, Tom McDonald, Howard Preston, and Richard Storm. "Roadway Lighting Shows Safety Benefits at Rural Intersections." ASCE Journal of Transportation Engineering (2010): 949-955.

Isebrands, Hillary, Shauna Hallmark, Zach Hans, Tom McDonald, Howard Preston, and Richard Storm. Safety Impacts of Street Lighting at Isolated Rural Intersections - Part II. Minnesota Department of Transportation, 2006.

Neuman, Timothy R., Ronald Pfeffer, Kevin L. Slack, Kelly Kennedy Hardy, Douglas W. Harwood, Ingrid B. Potts, Darren J. Torbic, and Emilia R. Kohlman Rabbani. NCHRP Report 500: Guidance for Implementation of the AASHTO Strategic Highway Safety Plan, Volume 5: A Guide for Addressing Unsignalized Intersections. National Highway Cooperative Research Program, 2003.

Preston, H. and T. Schoenecker. Safety Impacts of Street Lighting at Isolated Rural Intersections. Report MN/RC-1999-17. Minnesota Department of Transportation, 1999.

Roberts, S. E. and F. W. Walker. "Influence of Lighting on Accident Frequency at Highway Intersections." Transportation Research Record No. 562 (1976): 73-77.

SUDAS. 2014. Iowa Statewide Urban Design Standards. www.iowasudas.org/manuals/manual.cfm?manual=design.

Wortman, R. H., M. E. Lipinski, L. B. Fricke, W. P. Grimwade, and A. F. Kyle. Development of Warrants for Rural At-Grade Intersection Illumination. Illinois Cooperative Highway Research Program Series No. 135, University of Illinois, 1972.

Image: Rural roadway lighting

Rural roadway lighting (Hillary Isebrands et al./Institute for Transportation)

Image: Roadway lighting at a four-way rural intersection

Roadway lighting at a rural intersection (Hillary Isebrands et al./Institute for Transportation)


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