The vibration and impact of skewed multigirder bridges due to vehicles moving across rough bridge deck are studied. The bridges are modeled as grillage beam systems. The vehicle is simulated as a nonlinear vehicle model with 12 degrees of freedom according to the HS20-44 truck design loading specified in the American Associate of State Highway and Transportation Officials (AASHTO) specifications. Four classes of road surface roughness generated from power spectral density function for the approach roadways and bridge decks are used in the analysis. The impact factors of girders were obtained for one or two trucks (side by side). The effect of loading position in transverse direction, vehicle speed, angle of skew, and road surface roughness is studied. The analytic results show that the impact of girders will increase with increasing the angle of skew.