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TTCI evaluates the effects of adding superelevation to increase the allowable speed in mainline turnouts.
Researchers at Transportation Technology Center, Inc., (TTCI) evaluating the effects of adding superelevation to the diverging route of a mainline turnout have found that the changes in forces with superelevation are relatively small, with the superelevated region of the turnout being too short to reach steady state conditions and provide significant benefits.
The primary benefit of adding superelevation to a turnout is to allow for a smaller entry angle at the switch point, without reducing the allowable speed or increasing the overall length of a turnout. Several previous studies have shown that a smaller entry angle is the key to reducing the peak lateral forces for vehicles traversing the diverging route of a turnout.10
The tests were performed on a mainline turnout on the High Tonnage Loop at the Facility for Accelerated Service Testing (FAST) in Pueblo, Colo. A series of performance measurements including wheel/rail forces, track geometry and rail wear have been made during the first 480 million gross tons (mgt) of 315,000-pound car traffic over a No. 20 turnout retrofit with superelevation. Field test results of the reduced-entry angle, superelevated turnout have been largely as expected. Wear of the superelevated closure rails has been small, with no unusual gauge-face wear. The practical benefit of the superelevation is in allowing the use of a dynamically better turnout alignment without a penalty in allowable speed. Thus, the addition of superelevation to a low entry angle turnout will allow a railway to obtain the force reduction benefits of the low entry angle design without incurring a penalty in allowable train speed. Currently, there is a penalty in maximum allowable speed when using a low entry angle turnout as compared to a non-tangential alignment (AREMA-style) turnout.
There are two factors that limit allowable speed on the diverging route of turnouts. One is the superelevation unbalance in the diverging curve. This originated as a ride quality requirement for all curves on the railroad. The second is the potentially high lateral forces that can result from the large entry angle alignment typical in a freight railroad turnout. This is a safety limit that affects high entry angle alignment turnouts.
The addition of superelevation...