Guidelines for Traversability of Roadside Slopes (2019) / Chapter Skim
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Pages 113-125
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From page 113... ...
113 This chapter presents the development of the traversability guidelines using the results of the vehicle encroachment simulations. The first step in the development of the guidelines was to assign a weightage to each simulation case based on the probability of occurrence of the encroachment conditions used in that case.
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From page 114... ...
114 Guidelines for Traversability of Roadside Slopes encroachment angles was determined by calculating the ratio of the number of crash cases in that range and the total number of crashes in the database. This same approach was used to determine the probabilities for the encroachment speeds presented in Figure 7.2.
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Guideline Development 115 The departure angle, however, is the angle between the vehicle CG's trajectory and the roadway at the point of departure. In the tracking condition, the vehicle is facing in the direction that it is moving (see Figure 7.3a)
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116 Guidelines for Traversability of Roadside Slopes 7.1.3 Vehicle Type Probability Distribution To determine the probability distribution of the vehicles used in the simulation analyses, researchers used the automotive sales data for the United States for 2016 (42)
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Guideline Development 117 42.46% 15.34% 29.17% 13.03% SUVPickup TruckMidsize SedanSmall Car 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% Figure 7.6. Probability distribution for vehicle types used in simulation.
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From page 118... ...
118 Guidelines for Traversability of Roadside Slopes 7.2 Evaluation of Weighted Simulation Results Using the probability distributions developed for various encroachment parameters, the researchers weighted the outcome of each simulation and determined the combined probability of rollover for a specific roadside terrain. This process enabled the researchers to expose various trends, which were then used to develop the slope traversability guidelines.
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From page 119... ...
Guideline Development 119 7.2.2 Foreslope Width Figure 7.9 shows the influence of the foreslope width on the probability of rollover. It can be seen that the probability of rollover increases significantly when the foreslope width is increased from 8 to 16 ft, except for the 1V:10H foreslope, for which the rollover probability remains at approximately 10 percent for all foreslope widths.
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120 Guidelines for Traversability of Roadside Slopes (a)
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Guideline Development 121 The influence of foreslope width on rollover probability can have a significant effect on the rollover probability, especially for steeper slopes. Therefore, foreslope width was retained as one of the design parameters to be used in the slope traversability guidelines.
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122 Guidelines for Traversability of Roadside Slopes Figure 7.11. Probability of outcome for vehicles encroaching on slopes.
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Guideline Development 123 the probability of a recoverable encroachment decreases. While these trends are logical, it can be seen that for each foreslope type, there is a significant probability of any of the three outcomes.
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From page 124... ...
124 Guidelines for Traversability of Roadside Slopes Figure 7.12. Slope traversability guidelines showing the rollover probability for (a)
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Guideline Development 125 (a)
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