To determine the effects of vehicle load on the soil mass of an expressway subgrade soil in Shanxi Province, we investigated the dynamic response from vehicle loads, the seismic waveforms, and the soil dry density and confining pressures. The results show that the volume deformation of the subgrade soil increased with an increase in waveform ratio and vehicle load, the dynamic elastic modulus increased with an increase in dry density and confining pressure, and the damping ratio decreased with an increase in confining pressure.