To investigate relations between dynamic wheel loads of multi-axle vehicles on highway bridges and dynamic responses of bridge due to the vehicular loading, a three-dimensional dynamic analysis is carried out. Simultaneous differential equations for a coupling vibration of bridge and moving vehicle including roadway roughness are derived by means of modal analysis. The analytical wheel loads of vehicle model and responses of bridges are compared with experimental ones, to verify a validity of presented analytical procedure. Parametric investigations show that there exists resemblance between bounce motion of vehicle and bridge response. It can also be seen that the RMS based dynamic factor of dynamic wheel load can give an important information to predict the variation of impact factor of bridge due to speed condition as well as speed parameter.