Guidelines for Traversability of Roadside Slopes (2019) / Chapter Skim
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3 Run-off-road (ROR) traffic crashes account for almost one-third of the deaths and serious injuries each year on U.S.
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4 Guidelines for Traversability of Roadside Slopes Rollover is obviously the most consequential and deadly event for errant vehicles that involved ditches and earth embankments as the FHE. Slopes in ditches and embankments are expected to have played a key role for these rollover crashes to occur.
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Literature Review 5 In 1995, Viner analyzed national crash data to define the nature and importance of the problem of ROR vehicles that rolled over on slopes, including ditches and embankments (2)
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6 Guidelines for Traversability of Roadside Slopes finding was consistent between the analysis results from the FARS data and from the NASS GES data. Viner found that most vehicles that rolled over on sideslopes and ditches were skidding (or non-tracking)
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Literature Review 7 the outside does not seem to require as flat a slope nor as wide a clear zone as sharper curves. HVOSM studies of the cross-slope break on highway curves showed that driver control is sensitive to the shoulder slope.
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8 Guidelines for Traversability of Roadside Slopes flatter. Foreslope ratios ranging from 1V:3H up to 1V:4H are considered to be non-recoverable but traversable.
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Literature Review 9 • When the cost of a continuous flat slope is prohibitive, the area adjacent to the roadway should be reasonably flat. • Slope combination should be selected with the objective of limiting injury to unrestrained occupants and limiting vehicle damage during the traversal.
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10 Guidelines for Traversability of Roadside Slopes probability as a function of sideslope ratio. Generally speaking, the percentage of vehicle encroachments resulting in overturn increases as the steepness of the sideslope increases.
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Literature Review 11 a 25-degree encroachment angle, bumper-to-terrain contact and rear overhang drag were observed in all tests above 40 mph. In the absence of a steering and braking input, very little redirection was observed in the vehicle as it traversed a ditch.
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12 Guidelines for Traversability of Roadside Slopes vehicles. In most of the computer runs, the vehicle was directed off the travelway in a tracking condition at an encroachment angle of 15 degrees and an encroachment speed of 60 mph.
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Literature Review 13 stability. For example, the effect of horizontal curvature can be quantified by comparing the lateral extent of encroachment obtained for a curved section of roadway with that for a tangent section of roadway having similar roadside characteristics.
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14 Guidelines for Traversability of Roadside Slopes the exceedance curves can be used to determine the percentage of encroachments that will exceed a certain lateral distance. The simulation runs conducted for the adjustment variables were analyzed in the same manner as the baseline runs.
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Literature Review 15 85th percentile design encroachment conditions for both reported and unreported accidents were equivalent to the 70th percentile impact conditions for reported accidents. Using this approach, the lateral speeds for 53 accidents on rural arterial highways were calculated and the resulting data was fitted with a logistic normal distribution.
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16 Guidelines for Traversability of Roadside Slopes A total of four rollovers were observed for the impact conditions investigated: two rollovers happened with a free running vehicle, one was the result of steering input while the vehicle was in the ditch, and one was caused by impact with the low barrier placed in the bottom of the ditch. From the tests, it was observed that small cars rolled over when entering the ditch at 10 degrees and 80 km/h.
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Literature Review 17 2.3 Vehicle Testing with Remote Control Driver Input Texas A&M Transportation Institute has conducted two projects for NHTSA and the U.S. DOT where remote controlled input was applied for vehicle control and maneuvering.
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18 Guidelines for Traversability of Roadside Slopes properties of the vehicle. This simulated a real-world avoidance maneuver situation where an extreme turn is required suddenly.
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Literature Review 19 In the early 1980s, TTI conducted a series of embankment traversal tests as part of a project aimed at evaluating the performance limits of guardrails, median barriers, and embankments for different classes of vehicles and impact conditions (22)
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