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Cost-Effectiveness of Driveway Slope Improvements




Edward Post, Richard Ruby, Patrick McCoy, David Coolidge




Little attention has been given to the hazard of driveway fill slopes located along the roadsides of non-controlled and limited access rural high-ways. The severity of a standard size automobile (3,800 lb) traversing driveway slopes under the run-off-the-road encroachment conditions of 55 mph and 10 deg was investigated using the Highway-Vehicle-Object-Simulation-Model (HVOSM) in a free-wheeling steer mode. The results of a cost-effectiveness analysis on improving a typical driveway slope from a 3:1 to flatter slopes indicated that: (a) the 8:1 slope improvement was the most cost-effective alternative and could be made with 95 percent confidence that it would result in a reduction of injuries, (b) the 10:1 slope improvement alternative was not cost-effective, and (c) driveway improvement alternatives without underdrainage were more cost-effective than those with underdrainage. The injury probabilities used in this study were based on the magnitude of the computed resultant automobile accelerations averaged over a time duration of 50 msec, except rollovers were assigned an injury probability of one. The rate of rollovers decreased as the driveway slopes were flattened with none occurring on slopes flatter than 6:1.


Safety, Driveways, Encroachments, Auto-Simulation, Cost-Effectiveness

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