Wheel ruts on paved roads affect the maneuverability of a vehicle and sometimes trigger fatal accidents. At present, however, not enough is known about the cause of this unstable maneuverability on a rutted road. It is the purpose of this paper to provide some information on the dynamic behavior of a vehicle running on a rutted road. In order to evaluate the stability and controllability of a vehicle on a rutted road, we performed various running tests both on a rutted road and on a flat road.
Based on analyses using root-mean-squared (rms) values and the Developing Spectrum, the following conclusions were obtained: (1) RMS values for the vehicular motion on a rutted road are much greater than those on a flat road; (2) low-frequency contents below 1 Hz play an important role in the behavior of the vehicle on a rutted road; (3) visual guidance by ruts occasionally leads to stable straight runnings on a rutted road; and (4) the severer the lane-changing conditions, the larger the interaction between sprung mass and unsprung masses.