In the last few years, a growing interest towards structural safety of existing infrastructures has been paid. Due to very large number of structures, the scientific community is asked to provide innovative solutions that are both sustainable and reliable from the economical as well as technical point of view. This paper presents the case of Quarto bridge, selected as case study in an Italian research project for Risks and Safety Management of Infrastructures at Regional Scale (GRISIS). The structure is a railway viaduct on an urban train line, located in the Northern metropolitan area of Naples. It consists of 45 simply-supported prestressed girders sustained by reinforced concrete piers, for a total length of approximately one kilometer. According to the project, the viaduct was equipped with an on-site monitoring system for near-real-time mitigation of seismic risk. The system involves some innovative, low-cost, sensors developed and installed to be tested on the field. This paper describes the monitoring system and the implemented strategies for risk mitigation referring to a single beam-column system but its application can be potentially replicated and implemented for large scale mitigation strategies.