TTC OPERATED BY ENSCO
High-Speed Adjustable Perturbation Test Track for Vehicle Testing at the Transportation Technology Center Ground Truth Measurement Advances Research Radim Bruzek, R&D Program Manager, ENSCO, Inc., Springfield, VA Sean Woods, R&D Project Manager, ENSCO, Inc., Pueblo, CO Jennifer Zahacewski, Project Manager, ENSCO, Inc., Chambersburg, PA Alexandra D’Andrea, Program Manager, Track Research Division, Federal Railroad Administration Office of Research, Development, and Technology, Washington, DC
Figure 1. HS-APTT at the RTT Loop at the TTC
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everal years ago, the Federal Railroad Administration (FRA) installed a specially designed adjustable track at the Transportation Technology Center (TTC) in Pueblo, Colo. This track, referred to as the High-Speed Adjustable Perturbation Test Track (HS-APTT), can be configured to introduce known geometry perturbations. The HS-APTT, shown in Figure 1, consists of a 500-foot-long tangent slab track within the Railroad Test Track Loop (RTT) with
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specially designed steel cross ties, tie plates, and fasteners which allow adjustments to the profile, alignment, crosslevel, and gauge. Vertical deviations, up to a maximum of ±2 inches can be created by installing shim plates between the tie and tie plate in increments of 1/16-inch. Lateral deviations, up to a maximum of ±1.5 inches, are made by moving the tie plate to the gauge or field sides in increments of 1/4-inch. The adjustment mechanism is illustrated in Figure 2.
Profile, alignment, gauge, and crosslevel perturbations with desired amplitudes and wavelengths are introduced into the track by making required adjustments at multiple ties. In addition, track properties such as resiliency and damping can be adjusted and controlled. The ability to precisely introduce geometry perturbations into the track allows researchers to study vehicle response to known track inputs and to evaluate the accuracy of various Track Geometry Measurement Systems (TGMS). To use the adjustable slab track as a controlled test bed, the introduced track geometry must be precisely known. The process of introducing perturbations into the track does provide a high degree of control over the geometry. However, inconsistencies in the slab and small variations in the fasteners result in slight deviations between the true installed geometry and the installation plan. Therefore, geometry must be measured directly, as opposed to being inferred from the configuration of the track fasteners and tie plates. The process of precisely determining the actual track geometry is known as ground truth measurement. This ground truth is then used as the standard for assessing the accuracy of a track geometry system or for any other uses of the adjustable slab track. Initially the ground truth track geometry was determined using total stationbased surveying approaches. However, this process was time consuming and susceptible to loss of accuracy due to wind and heat mirage. Additionally, this approach was not accurate enough to evaluate typical vehicle mounted track measurement systems. A fast and accurate method of measuring the ground truth track geometry was needed. FRA contracted ENSCO to evaluate existing solutions for ground truth measurement of the HS-APTT. The evaluation criteria were ease of setup and use, high accuracy, and the ability to independently verify the geometry parameters. ENSCO’s investigation of existing survey technologies found no viable solution, mainly due to insufficient accuracy over the length of the 500‐foot section of track, and concerns about traceability of the measurements. Intellectual rtands.com