A two-degrees-of-freedom quarter-vehicle suspension model is used in this work. The road is modelled as a Bernoulli—Euler beam with simply supported ends on a linear viscoelastic Kelvin foundation. Thus a two-dimensional vehicle—road system is built. Analytical solutions of the vehicle body, wheel, and road's dynamic response are derived by the mode superposition method. The solutions are directed to analyse the distribution of road displacement and the concept of second road excitation on the vehicle is proposed. Influences of the second road excitation on the vehicle suspension displacement, vehicle body acceleration, and tyre force are investigated. It is found that second road excitation should be considered in vehicle dynamic analysis when a heavy vehicle runs on a smooth highway road.