The objective of this paper is to investigate the dynamic response of a rigid frame bridge to two trucks (side by side) passing over the rough bridge deck. The rigid frame bridge is designed according to AASHTO specifications and modeled as a space bar system. The analytic truck is modeled as a nonlinear system with twelve degrees of freedom according to the HS20-44 truck design loading specified in the AASHTO specifications. The road surface roughnesses of the approach roadways and bridge decks are considered in the analysis. Maximum dynamic responses of each rigid frame at different sections are determined for two trucks through changing their transverse positions with different speeds and road surface roughnesses.