The Vibration Test Unit (VTU) of the Rail Dynamics Laboratory at Pueblo, Colorado, can be used for vibration testing of railroad vehicles with revenue track input. Until recently, the usual source of track geometry input to the VTU consisted of Plasser car digital tape recordings of track displacements as a function of distance along the track. A second track geometry input to the VTU was developed based on the Locomotive Track Hazard Dector (LTHD) concept, which produced displacement history data obtained by processing the time histories of special axle-mounted accelerometers. Tests were conducted at the Transportation Test Center, Pueblo, Colorado, to validate a suitable form of input to the VTU which closely duplicate the actual revenue track input. The results indicated that the responses of the test vehicle on the VTU, excited with input based on the LTHD concept, compared closely with the corresponding responses monitored on the actual track, while the Plasser time history input to the VTU produced responses which showed considerable variation at speeds 30 mph and above in both amplitude levels and frequency content. The close agreement between the responses during the track tests and VTU runs with the LTHD time history input has opened up a realm of testing capabilities of the VTU for freight car structure and lading damage evaluation on a given revenue track.

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