PhD Defense by Franklin E. Gbologah

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  • Date/Time:
    • Monday November 2, 2015
      11:00 am - 1:00 pm
  • Location: ES&T Room L1120
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Summary Sentence: The Impacts of Illumination Levels on Nighttime Safety at Roundabouts

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School of Civil and Environmental Engineering



Ph.D. Thesis Defense Announcement


The Impacts of Illumination Levels on Nighttime Safety at Roundabouts



Franklin E. Gbologah



Dr. Michael O. Rodgers, CEE



Committee Members:

Dr. Adjo Kennedy - CEE; Dr. Randall Guensler - CEE; Dr. Michael Hunter - CEE;

Dr. Angshuman Guin – CEE; Dr. Brian Stone,  City and Regional Planning



Date & Time: November 2, 2016 at Noon

Location: ES&T Room L1120

Roundabouts are a proven safety countermeasure and must be considered as an alternative for all new intersections as well as for reconstruction, and/or rehabilitation of existing intersection that are federally funded. The Insurance Institute for Highway Safety (IIHS) reports that roundabouts typically experience 40 percent fewer vehicle collisions, 80 percent fewer injuries, and 90 percent fewer serious injuries/fatalities than their conventional counterparts in both urban and rural settings. These significant safety benefits are achieved by a speed reducing geometry which deflects the travel path of a vehicle around a raised central island along a the circular path. This deflected travel path implies that roundabouts may require visibility enhancing treatments to ensure that they can be safely negotiated by drivers, especially during nighttime conditions. Consequently, U.S. national guidelines recommend the systematic illumination of roundabouts in both rural and urban areas. However, in most countries around the world, rural roundabouts are kept unlit as indicated by a recent survey of international roundabout illumination policies and standards from 45 countries Roundabout illumination is expensive to both install and maintain with associated maintenance and power costs representing up to about 1.5 times the initial investment costs over a 15 year period. Given that most roundabouts in the US are being used to replace existing uncontrolled or stop-control intersections, which are normally kept unlit in rural areas, the associated costs of roundabout illumination imposed by the current guidelines could preclude the installation of a roundabout that would otherwise be safer than their conventional counterpart.

This study evaluates the link between roundabout crashes and different illumination levels. Previous research studies evaluating the linkage between illumination levels and intersection safety have been focused on conventional intersections or treated illumination as a binary (Yes/No) variable. However, even in the absence of any purpose-built roadway lighting there may be nearby ambient light sources (e.g. gas stations, houses, or stores) that may provide significant intersection illumination relative to truly unlit conditions. There is currently no repository of actual intersection illumination data. Therefore, this study developed and field-tested a method for determining these actual illumination levels using a calibrated digital single lens reflex (DSLR) camera. This procedure was used to collect actual intersection luminance from more than one hundred roundabouts and conventional intersections across Georgia. Crash data obtained from the Georgia Department of Transportation (GDOT) were analyzed along with these illumination data to evaluate the impact of different illumination levels on nighttime safety at roundabouts.

Existing protocols require the use of expensive high-precision luminance meters and are very time consuming. The measurement protocols developed in this study offer transportation agencies a fast and inexpensive method to both evaluate ambient illumination levels and to audit the adequacy of installed street lighting. The field tests from this study provide the basis for initial efforts to create an illumination specific quantitative crash modification factor (CMF) for both roundabouts and conventional. The current edition of the Highway Safety Manual currently lacks this important safety parameter. This work further contributes a documented database of both conventional intersections and roundabouts illumination levels in the state of Georgia that can be used in future years to refine the initial results of this study. A well established relationship between illumination and safety will allow practitioners to determine the most appropriate illumination level to maximize the benefit-to-cost ratio for intersection safety.

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  • Created By: Tatianna Richardson
  • Workflow Status: Published
  • Created On: Oct 16, 2015 - 11:09am
  • Last Updated: Oct 7, 2016 - 10:14pm