A new three-dimensional vehicle with tandem axels is developed to determine dynamic response of bridge deck under load applying truck. The vehicle is modeled by a dynamic system with 9 degrees of freedom to accurately simulate the disposition and the intensity of loads on the bridge deck. The bridge deck is modeled by an orthotropic multi-span plate. The road surface irregularities are modeled by a random function characterized by a spectral roughness coefficient and power spectral density. The modal method is used to solve the equation of motion of the bridge deck. Equations of motion of the vehicle are obtained using the virtual work principle. The coupled equations of motion vehicle/bridge deck are integrated numerically by Newmark’s method. A computational algorithm is then elaborated to solve the integrated equations of motion with iterative process. A numerical example is presented. The resulting distribution of the Dynamic Amplification Factor (DAF) on the bridge deck does not reflect any particular trend, because high values can be obtained at points where the vertical displacement is small. The DAF is significant only under the interaction force. Thus, the road surface roughness was shown to have a significant influence on the dynamic vehicle/bridge deck interaction forces.