Signs located on overpasses have been observed to undergo significant vibrations. The excitation force driving the vibrations is the dynamic oscillation of the highway bridge during the passage of loaded trucks. The researchers involved in this project will record accelerations causing the oscillations of prestressed girder bridges under traffic loading. They will use instrumentation along and across the bridge to determine the mode shape of the bridge as well as the frequency and magnitude of the dynamic oscillation of the bridge. The researchers will use the data to develop dynamic finite element computer software models that will be used to evaluate mounting sign locations on overpasses.