“…2-axle, 3-axle, 4-axle, 5-axle, and 6-axle vehicles are presented as the oscillatory dynamic systems with 7, 9, 11, 13, and 15 DoFs, respectively. The simplified models of the 2-axle vehicle are shown in Figure 6 Based on the D'Alembert principle, the differential equations of motion for the 2-axle vehicle model can be presented by the following equations (11–14) (Yu et al, 2018). The vertical motion of the vehicle body for the 2-axle vehicleThe pitching motion of the vehicle body for the 2-axle vehicleThe rolling motion of the vehicle body for the 2-axle vehicleThe vertical motion of the wheel for the 2-axle vehiclewhere m b is the mass of the vehicle body; m wi ( i = 1,2,3,4) is the mass of the i -th wheel; a x is the heading acceleration of the vehicle, which can consider the acceleration or deceleration of the vehicles under the control of the drivers; Ix, Iy are the mass moment of inertia of the vehicle body around the x,y axes, respectively; ks2i,kt2i(i=1,2,3,4) is the vertical stiffness of the i -th suspension spring and tire of the two-axle vehicle; Cs2i,Ct2i(i=1,2,3,4) is the vertical damping coefficient of the i -th suspension spring and tire of the two-axle vehicle; a,b is the distance between the vehicle’s mass center and the front and rear axles, respectively; t w is the transverse distance between the coaxial tire and the mass center; h is the vertical distance between the vehicle’s mass center and each wheel; I y , I x is the angular displacement of the vehicle body around the y and x axes, respectively; Z b is the vertical displacement of the vehicle body; zwi(i=1,2,3,4) is the vertical displacement of the i -th wheel; Z gi (i=1,2,3,4) is the road surface height of the i -th tire contact position (sum of surface roughness height and vertical response of bridge; …”