There is a significant need to examine precisely the conditions of concrete road bridges because of the increasing traffic and axle loads and the fact that most existing bridges were not designed with respect to fatigue. In-situ investigations are challenging in terms of long-term monitoring of deformations and displacements, the difficulty of access to relevant zones of bridges in service, and limitations in current measurement methods and techniques. This paper presents the case study of a specifically designed continuous monitoring system, installed in the reinforced-concrete slab of a 60-year road viaduct, in order to detect possible initial fatigue damaging events due to traffic loading, since the slab currently does not show any sign of fatigue damage in terms of cracks. The originality of the paper lies in the combination and synchronization of four nondestructive-testing techniques, i.e. an acoustic emission system, an ultrasonic system, strain gauges, and thermocouples, to perform long-term monitoring of the RC deck slab of this viaduct under service conditions. It is found that the monitoring system is efficient to detect acoustic emission parameters as a function of traffic and temperature variations.