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Citation |
Farber EI. Transp. Res. Rec. 1987; 1122: 57-67. |
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Copyright |
(Copyright © 1987, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing) |
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DOI |
unavailable |
PMID |
unavailable |
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Abstract |
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. Language: en |
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Keywords |
ROADS AND STREETS; HIGHWAY SYSTEMS - Accident Prevention; MATHEMATICAL STATISTICS - Monte Carlo Methods |