United States Department of Transportation
i
Improved Spiral Geometry for High Speed Rail [Research Results]
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2008-01-01
[PDF-142.04 KB]
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Abstract:A different shape of spiral section for transitioning from tangent to curved track was tested on the Northeast Corridor in a 0.925-degree curve near Guilford, CT, where typical operating speed for Amtrak's Acela trains is 125 mph. The modified spiral geometry was intended to reduce lateral forces and improve ride quality for high speed trains when entering and exiting curves. The modified design causes a train to rotate around its center of gravity as it leans into a curve, rather than centering rotation at the top-of-rail as does a conventional railroad spiral. Ride quality and force measurements were made before and shortly after spiral modification, and 1 year later. Compared to conventional geometry, initial and final measurements showed that the modified spirals reduced peak-to-peak lateral accelerations in the car body by 41 percent. Lateral wheel-rail force measurements from two instrumented wheelsets of an Acela power car showed a reduction in root-mean-square (RMS) net axle lateral forces of about 33 percent. Initially, truck lateral peak-to-peak acceleration dropped by 38 percent, but after 1 year, these accelerations returned to the pre-modification levels. At the test site, the modified spiral geometry was applied without the need to change rail length. The resulting shape and rate of superelevation change also fall within existing Federal Railroad Administration (FRA) track safety standard allowances. Amtrak plans to continue this study by installing the modified spiral geometry on at least two additional curves for further evaluation.
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