Investigation of driver speed choice and crash characteristics during low visibility events : final report.

Details

• Creators:
  McCann, Katie ; Fontaine, Michael D.
• Corporate Creators:
  Virginia Transportation Research Council (VTRC)
• Corporate Contributors:
  Virginia. Dept. of Transportation ; United States. Federal Highway Administration
• Subject/TRT Terms:
  • Algorithms
  • Behavior
  • Crash data
  • Drivers
  • Fog
  • Operating speed
  • Standard deviation
  • Variable speed limits
  • Visibility
  • Fog
  More +
• Publication/ Report Number:
  VTRC 17-R4
• Resource Type:
  Tech Report
• Geographical Coverage:
  United States ; Virginia
• Edition:
  Final report
• Corporate Publisher:
  Virginia. Dept. of Transportation
• Abstract:
  In Virginia, sections of I-77 and I-64 in mountainous parts of the state have significant recurring fog events. These ; locations have also been the sites of several chain reaction crashes involving more than 50 vehicles during fog. These crashes ; were typically caused by drivers traveling too fast for the visibility conditions. To improve safety on the I-77 corridor, the ; Virginia Department of Transportation constructed a variable speed limit (VSL) system that posts dynamic speed limits based on ; the visibility condition. As of April 2016, the system was undergoing pre-deployment testing. Before the system was activated, ; it was important to understand existing driver speed choice behavior during low visibility conditions. It was possible that posting ; a VSL speed based only on the stopping sight distance (SSD) could create significant speed variance and decrease safety if ; drivers were driving much faster than conditions would warrant. In this study, crash, speed, and visibility data were examined at ; several locations on I-64 and I-77 where there were recurring fog events. ; The crash history for I-77 revealed that crashes during low visibility conditions were more likely to be severe and ; involve more than two vehicles than crashes during clear conditions. Mean speed analysis found that observed mean speeds ; exceeded safe speeds for all low visibility conditions and at all sites. In the worst visibility conditions, drivers often exceeded the ; safe speed by more than 20 mph. Standard deviation analysis found that speed variance did not increase as visibility decreased ; on I-77, but for several locations on I-64, the standard deviation was different during low visibility when compared to clear ; conditions. ; Models were developed to allow a better understanding of the relationship between speed and visibility. The models ; showed that although motorists reduce their speeds in low visibility, there is still a significant differential between observed ; speeds and the safe speed calculated using the SSD. The models showed that speeds for I-64 were much less sensitive to ; changes in visibility compared to I-77. A possible explanation for this difference is the presence of illuminated in-pavement ; markers on I-64. The improved delineation provided by these markers during foggy conditions may cause drivers to perceive ; less of a need to reduce speed during limited visibility. It is also possible that mean speeds in low visibility conditions are higher ; on I-64 because of the regular commuters who may be more comfortable driving during foggy conditions. ; The observed driver behavior from this study is being used as a basis for the VSL control algorithm that is being ; implemented in the field. A primary concern of the operators of the VSL system is that it will not be heeded by all motorists and ; thus will result in increased speed variance in foggy conditions. The developed model was used to create a VSL control ; algorithm to help bridge the gap between current driver behavior and safe speed. It is recommended that future VSL system ; deployments reflect existing driver behavior in the initial algorithms as well. After VSL activation, speed and crash data for I-77 ; should be analyzed to determine the operational and safety effects of the system. If the system on I-77 reduces the frequency and ; severity of crashes, improves speed limit compliance, and reduces speed variance, a similar system should be developed for I-64 ; using the current driver behavior models from this study as part of the initial algorithm.
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• Format:
  PDF
• Funding:
  106414
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/31334/dot_31334_DS1.pdf
• File Type:
  [PDF - 3.10 MB]
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha256:02436032418a75700cc11572a2b0faf9afd68ce4cb912c7348bc09e77bc24f74