Highway bridges undergo rapid deterioration in both condition and safety under the influence of aggressive environmental factors and increasing traffic loads. Timely and adequate maintenance interventions are therefore crucial to ensure the functionality of existing bridges in a network. Under budget constraints, it is important to prioritize maintenance needs to bridges that are most significant to the functionality of the entire network. In this paper, the network-level bridge maintenance-planning problem is formulated as a combinatorial optimization problem and an algorithm is developed to select and allocate maintenance interventions of different types among networked bridges over a specified time horizon under the assumption of annual inspections. As an illustration example, the optimization procedure is applied to a heterogeneous 5-bridge network. The results show that the proposed maintenance planning procedure has the capability of prioritizing scarce maintenance needs to deteriorating bridges that are most crucial to the network performance.