MODELING CONFLICTS AT INTERSECTIONS HIDDEN BY VERTICAL CURVES

In this paper, a model that estimates the relative hazard to passenger cars stopping to turn left at an intersection hidden by a vertical curve is described. Because of the limited sight distance, following cars might not be able to see the left-turning vehicle in time to stop on wet pavement. Monte Carlo methods are used to estimate the relative frequency of such hazardous incidents as a function of traffic volume and sight distance. These incidents are serious conflict situations in which an accident could not be avoided by braking alone. Left-turn gap acceptance and headway distributions in opposing traffic are used in the model to determine the random delay experienced by left-turning passenger cars. Other random variables addressed in the model are traffic speeds, headways of cars following the left-turning car, and the perception reaction time of following car drivers. The results indicate that the conflict rates increase rapidly with decreasing sight distance. Conflicts increase with hourly volume up to about 600 vph and then level off or decrease. Values range from 9 conflicts per 10,000 wet-pavement left turns at 150 vph at sites with sight distance based on the 1965 AASHO Bluebook to 486 conflicts per 10,000 wet-pavement left turns at 750 vph and substandard sight distance. Assuming that 2 percent of traffic turns left and pavements are wet 15 percent of the time, annual totals range from 0.32 to 101 conflicts per year, depending on sight distance and daily volume. Conflict rates are substantially reduced by decreases in reaction time and speed, which might be produced by appropriate signing, and increases in pavement friction. In combination, these countermeasures are at least as effective in reducing conflicts at sites with substandard sight distance as bringing the sight distance up to standard would be.

• Record URL:
  • http://onlinepubs.trb.org/Onlinepubs/trr/1987/1122/1122-007.pdf
• Record URL:
  • https://scholar.google.com/scholar_lookup?title=MODELING+CONFLICTS+AT+INTERSECTIONS+HIDDEN+BY+VERTICAL+CURVES&author=E.+Farber&publication_year=1987
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• Supplemental Notes:
  • Publication of this paper sponsored by Committee on Operational Effects of Geometrics. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved
• Authors:
  • Farber, Eugene I
• Publication Date: 1987

Media Info

• Media Type: Print
• Features: Figures; Maps; References; Tables;
• Pagination: pp 57-67
• Monograph Title: Geometric design and operational effects
• Serial:
  • Transportation Research Record
  • Issue Number: 1122
  • Publisher: Transportation Research Board
  • ISSN: 0361-1981

Subject/Index Terms

• TRT Terms: Countermeasures; Curves (Geometry); Estimating; Hazards; Headways; Intersections; Left turns; Measures of effectiveness; Monte Carlo method; Pavements; Reaction time; Sight distance; Simulation; Traffic conflicts; Traffic speed; Traffic volume; Wet weather
• Uncontrolled Terms: Effectiveness; Vertical curvature; Wet pavements
• Subject Areas: Design; Highways; Pavements; Planning and Forecasting; Safety and Human Factors; I21: Planning of Transport Infrastructure;

Filing Info

• Accession Number: 00468656
• Record Type: Publication
• ISBN: 030904474x
• Files: TRIS, TRB, ATRI
• Created Date: May 31 1988 12:00AM