Abstract: The dynamic behavior of bridge structures under moving vehicular loads is studied. The vehicle is modeled as a four-DOF system with linear suspensions and tire flexibility, and the bridge is modeled as a continuous Euler-Bernoulli beam simply supported at both ends. A mathematical model is adopted to describe the roughness of the contact surface between the vehicles and the bridge. The partial differential equation governing coupled vibration of moving vehicles and beam structure is derived. The equation is solved in the time domain by modal analysis and Newmark method. In the numerical examples, the impact coefficient of the bridge is obtained. The shear force and bending moment of the beam are calculated. The dynamic responses of the bridge are simulated with different loads, vehicle speeds, bridge surface roughness, and the span of the beam.