ABSTRACT
Assessing existing bridges requires balancing the risk of failure and mitigation costs. Economic and human safety aspects are considered when deriving an optimal or acceptable level of safety. Additionally, an absolute human safety criterion may provide an upper risk limit, and this study aims to clarify its role and criticality. Although human safety is included in the marginal life-saving criteria through the life quality index and the societal willingness to pay for one additional saved life, this does not guarantee the safety of individuals. The rationale behind this is that even though it would be worthwhile to sacrifice human safety because the average expected risk to humans is low compared to the cost of mitigating the risk, exposing individuals to adverse risks is not ethical. With this contribution, we discuss the relation between individual risk and structural risk and identify factors contributing to the relative importance of the absolute human safety criterion compared to the cost-benefit and marginal life-saving criteria for existing road bridges. From these factors, we derive classes of cases for which the absolute human safety criterion can safely be ignored and cases when it governs the assessment. The results are useful for future reliability- and risk-based assessments of bridges.
