Sustainability assessment is very topical these days and also for bridges several approaches are under development. Although holistic analyses often work with checklists and qualitative assessment instruments, some strong and reliable assessment methods are regularly applied when performing sustainability analyses. Two of them are life-cycle costing and external cost calculation. The method of life-cycle cost calculation is established for bridges for at least 15 years and external costs are often partly considered by incorporating user costs in the analyses. Nevertheless, comparative life-cycle cost calculations and external cost analyses are usually not applied in bridge building projects. The existing publications often treat life-cycle costs as a framework and not as a calculation method. This paper presents a comparative LCC analysis for three different highway bridges with a special focus on steel bridges. The relevance of the system boundaries, the influence of different maintenance strategies as well as input variables like marginal cost rates and cost approaches is discussed. The results help to identify most important cost drivers and to assess the impacts within the life-cycle.