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VEHICLE CONTROLLABILITY IN A PAVEMENT/SHOULDER EDGE CLIMB MANEUVER

The results are described of a test program to evaluate various roadway disturbances in the driving environment, in order to pare down the list of possible disturbances to the worst cases, identify handling problem areas, find response parameters, and compare responses of different vehicles which might influence the results. The program provided an accident data analysis, survey questionnaire results, and full-scale test results; the pavement/shoulder dropoff (requiring an edge climb maneuver) was found to be the most severe and most likely disturbance to result in lane exceedance. This occurs when the vehicle is scrubbing one set of tires on the shoulder edge (or encountering the edge at too shallow an angle for climb), thereby requiring the driver to apply a large steering deflection to get the car back on the pavement. In this case, the vehicle will spin out if the speed is high enough. Road tests were performed with four passenger cars to get objective vehicle response performance measures as a function of vehicle type, shoulder height, and tire parameters (construction, wear, and pressure). The tests were divided into two categories: closed-loop and open-loop. In the closed-loop tests the effects of the driver, the vehicle, and the environment were all included, whereas in the open-loop tests only the basic vehicle response to the shoulder climb was considered. The closed-loop test with naive drivers in several different cars showed speed to be the critical factor for exceeding a lane boundary after an edge climb from a scrubbing condition. A modified open-loop handling parameter was defined, from which it is possible to predict the closed-loop critical speeds without having to perform closed-loop tests with naive drivers. Steering wheel required to force a vehicle to climb a curb from a scrub condition is independent of speed, but increases with increasing shoulder height. The severity of the shoulder climb maneuver is markedly reduced if the climbing tires are displaced by as little as 6 in. from the shoulder. Steering wheel required to climb from a scrub condition is a function of tire characteristics (worn tires climb easier than new ones; radials and those with low pressure also require less steering). For shallow encounter angles the closing velocity required climb also varies with tire wear (new tires climb at lower closing velocities than worn tires). When in a right turn with the right wheels on the shoulder, the criticality of the situation is significantly reduced over the straight-line case. However, in a left turn the control problem is virtually eliminated since a scrub condition cannot be easily maintained.

  • Availability:
  • Supplemental Notes:
    • Presented at SAE Passenger Car Meeting, Detroit, 26-30 September 1977. See also HS-802 210--HS-802 212.
  • Corporate Authors:

    Society of Automotive Engineers (SAE)

    400 Commonwealth Drive
    Warrendale, PA  United States  15096
  • Authors:
    • Klein, R H
    • JOHNSON, W A
  • Publication Date: 1978

Media Info

Subject/Index Terms

Filing Info

  • Accession Number: 00396326
  • Record Type: Publication
  • Source Agency: National Highway Traffic Safety Administration
  • Report/Paper Numbers: SAE 780620, HS-025 524U
  • Contract Numbers: DOT-HS-5-01223
  • Files: HSL, ATRI, USDOT
  • Created Date: Aug 31 1985 12:00AM