The aim of the work presented here was to provide enhanced assessment methods that are able to prove higher load carrying capacities and longer service lives for existing concrete railway bridges. One main objective was to develop methods for non-linear analysis since this provides the greatest potential to discover any additional sources for load carrying capacity, and gives an improved understanding of the structural response. Another main objective was to provide methods for assessing deteriorated concrete bridge. Recommendations are given regarding the effect of reinforcement corrosion, particularly on anchorage capacity. Furthermore, a methodology for improved assessment of the remaining fatigue life of short-span concrete bridges and secondary elements is presented. Other topics treated are evaluation of material properties, simplified methods for structural analysis and the bending-shear-torsion interaction