Service structures, such as sign structures and lighting poles installed on highway bridges, are often subjected to stress cycles due to traffic-induced vibration, and this causes fatigue problems. Vibration and stress measurements were carried out for frame structures on a viaduct. The viaduct was structurally modified from a simple girder to 3-span continuous girder to increase seismic resistance. The natural frequency of the first bending mode of the simple girder of 3.78Hz decreases to 3.58Hz with elastomeric bearing and 3.58Hz for 3-span continuous girders. Fatigue life calculated from stress range histogram was reduced, when the natural frequency of the viaduct was near to that of the service structures.