This paper presents dynamic analyses of railway bridges traversed by heavy freight trains, with application to the iron ore line in the North of Sweden. The main objective is to show that the allowable axle load can be increased as a result of lower dynamic effects compared to current design codes, especially for short- and medium span bridges. Simulations are based on a 2D traintrack-bridge interaction model and a large set of sampled realistic track irregularities. Using a semi-probabilistic approach, the results show that for short span bridges the dynamic effects is less than 15% compared to more than 40% in current codes. For span lengths longer than 10 m the dynamic effects are less than 5% according to the simulations. A parametric study shows that the dynamic effects are proportional to the standard deviation of the track irregularities and that the main governing effects of the train is the un-sprung mass.