Evaluating and upgrading existing structures becomes more and more important. For a large part of the existing infrastructure and buildings the design life has been reached or will be reached in the near future. These structures need to be reassessed in order to find out whether the safety requirements are met. Not only for new structures but also for the existing stock the Eurocodes are starting point for the assessment of the safety. However, it would be uneconomical to require all existing buildings and civil engineering works like bridges to comply fully with these new codes and corresponding safety levels. The assessment of existing structures therefore differs from the design situation. This paper describes the main differences with respect to the relevant reliability requirements and develops a set of partial factors to be used in the case of the reassessment of existing bridges under traffic load.