In the last few years, the real-time monitoring of civil infrastructures has become an essential tool for the safety inspection, the design and planning of maintenance. In this context, the implementation of optic fiber sensors embedded in the structural elements is particularly useful to check strains and displacements and assess the structural safety level. In this paper, a methodology aimed at the control of the safety and serviceability level of a Prestressed Reinforced Concrete Viaduct located in the city of Bari (Italy) is presented. The procedure is based on information acquired by fiber optic monitoring system implemented during the construction of the bridge. The processing of the data provided by the sensors at different times of the execution has allowed the appraisal of the strain variations related to the load increments and to the stress losses in the different phases and the comparison with the theoretical values. This comparison enables a double check: control in the construction phases, safety in the service life.