This paper aims to investigate the optimal transverse position for overweight trucks to cross the simply-supported multi-girder bridges. Finite element analysis is performed for a group of prefabricated concrete T-beam bridges commonly used in China under the action of overweight trucks with varying transverse positions. The maximum bending stresses at the mid-span of the girders are extracted from finite element analysis and compared with each other. The optimal transverse position is determined from the point of optimizing the structural response. The effects of a few important parameters, including the length of bridge spans, number of girders and type of girder connections on the optimal transverse truck position are investigated. It is found that the transverse loading position of overweight trucks has a significant impact on the responses of multi-girder bridges. For the T-beam bridges with odd number of girders, the optimal transverse position for overweight trucks is in the middle between the center girder and the adjacent girder; for the T-beam bridges with even number of girders, the optimal transverse truck position is the centerline of the bridge. The influence of the girder connection condition on the bridge responses is significant.