Decision makers use bridge management systems to determine the optimal allocation of available resources. These systems are currently focused on the structural condition of deteriorating bridges with respect to traffic loads. Bridges, however, are affected by multiple hazards, such as flooding and earthquakes, and not only traffic loading. These multiple hazards should be considered in these management systems when determining the optimal intervention. A risk-based approach can be used to determine the optimal intervention for a bridge subjected to multiple hazards. It requires the determination of the likely ‘levels of service’ to be provided by the bridge, (e.g. both lanes of traffic open, only one lane of traffic open or both lanes closed), the evaluation of the probability of having these levels of service due to the multiple hazards as well as the consequences of each of these levels of service, and selecting the interventions to minimise the risk of inadequate service. This article gives the methodology to be used when determining the optimal intervention for a bridge affected by multiple hazards. The risk-based approach is illustrated using a simple example in which the optimal intervention of two interventions is found.