In the investigation of vehicle behavior resulting from traversal of the roadside, computer simulation validated by full-scale tests were used to investigate vehicle behavior at the three critical regions of the roadside: the hinge-point, the front slope, and the toe-of-slope including four ditch configurations Vehicle operating conditions included speeds from 40 to 80 mph, encroachment angles of 7, 15, and 25 degrees, and steer-control conditions simulating a free-wheeling vehicle and attempted return-to-the road maneuvers on the front slope. Details are given of the two criteria used to evaluate roadside traversal and the ditch evaluation curves developed for various severity indices. The findings revealed that the hinge point created by the planar intersection of slopes 3:1 to 10:1 produced no critically adverse effects. It was also found that although maximum vehicle roll angles were produced by crossing the hinge point, no traversals approached vehicle rollover. Return maneuvers can be accomplished without vehicle rollover on smooth, firm embankments 3:1 or flatter at speeds to 80 mph and encroachment angles of 15 degrees. To permit recovery, a coeffccient of friction of at least 0.6 must be available and embankment surfaces must be relatively uniform. Almost no returns can be executed when the coefficient is as low as 0.2 Soft or rutted embankments can lead to rollover for return maneuvers at 60 mph. Toe-of slope region findings relate to the severity of traversal of ditches, trapezoidal ditch configuration, and steep front slopes. These findings are discussed in detail. A series of charts is included for selecting traversable slope-ditch combinations.
Abstract