In this paper the dynamic amplification factors and the equivalent uniform distribution load (EUDL) of bridges under random traffic flows are analyzed. The simply supported beam is selected as the bridge model. Two types of road roughness: road with step surfaces and stochastic surfaces, are included in simulation. The plane truck model can be with simple lorry or double lorries with various random parameters. Both free and congested traffics in individual slow or fast lanes and two lanes are considered. The dynamic amplification factors and EUDL of bridges with some given span from Monte Carlo simulations are listed.