Examination of the Safety Impacts of Varying Fog Densities: A Case Study of I-77 in Virginia

Fog can represent a significant safety hazard for motorists. While several studies have examined how fog crashes differ from crashes in clear conditions, they have treated fog as a homogeneous condition and not considered the safety impact of varying fog densities. I-77 in Fancy Gap, Virginia was used as a case study to better understand how safety changes as a function of available visibility. This study used crash, speed, visibility, and traffic data to characterize typical fog events, determine differences in crash characteristics by the severity of fog, and determine how speed profiles change with the density of fog. The analysis found that crashes in fog are more likely to be severe and involve more than two vehicles, supporting the findings of prior studies. While drivers reduce their speed in fog, the mean speeds exceeded safe speeds under all fog conditions. Examination of crashes and speed profiles by severity of visibility reduction showed that the level of available visibility impacts safety. The analysis showed that the presence of any fog has a negative effect on safety, with differential effects being observed depending on the severity of visibility reduction. Safety worsened when visibility drops below the stopping sight distance for the roadways, and then further degraded when visibility dropped below 360 feet. The results show that safety impacts of fog are not uniform across fog densities, and that mitigation efforts should be focused on areas experiencing recurring dense fog.

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• Supplemental Notes:
  • This paper was sponsored by TRB committee ANB20 Standing Committee on Safety Data, Analysis and Evaluation.
• Corporate Authors:

  Transportation Research Board

  500 Fifth Street, NW
  Washington, DC  United States  20001
• Authors:
  • McCann, Katie
  • Fontaine, Michael D
• Conference:
  • Transportation Research Board 95th Annual Meeting
  • Location: Washington DC, United States
  • Date: 2016-1-10 to 2016-1-14
• Date: 2016

Language

• English

Media Info

• Media Type: Web
• Features: Figures; Maps; References; Tables;
• Pagination: 18p
• Monograph Title: TRB 95th Annual Meeting Compendium of Papers

Subject/Index Terms

• TRT Terms: Behavior; Crash causes; Fog; Speed; Stopping sight distance; Visibility; Weather conditions
• Identifier Terms: Interstate 77
• Geographic Terms: Fancy Gap (Virginia)
• Subject Areas: Highways; Safety and Human Factors; I80: Accident Studies; I83: Accidents and the Human Factor;

Filing Info

• Accession Number: 01588731
• Record Type: Publication
• Report/Paper Numbers: 16-1867
• Files: PRP, TRIS, TRB, ATRI
• Created Date: Jan 29 2016 9:32AM