Increasing speed through turnouts: a FRA-sponsored study looks at low-cost means to increase safe speeds through turnouts, by way of a retrofit or upgrade

Railway Track and Structures, July, 2004 by Clifford S. Bonaventura, Allan M. Zarembski, Joseph W. Palese, Donald R. Holfeld

* Single wheel L/V: < 1.0

* AAR Net Axle L/V: < 1.4

* FRA Net Axle L/V: < 0.5

* Truckside L/V: < 0.6

* Peak-to-peak lateral acceleration: < 0.5g

* Wheel unloading: > 10%

The predicted responses for the new set of designs were compared with the responses from other existing turnout configurations (AREMA, Tangential Geometry, etc.). These are illustrated in Figures 4 and 5, respectively, for L/V ratio and lateral acceleration. These figures show the results for the AREMA straight switch point design at its limiting speed of 36 mph, the AREMA curved point design at the speed limit of 51 mph, and the tangential geometry design (which is 20 feet longer than the AREMA standard) for a speed of 60 mph. In addition, the modified design (C0) is used at three different speeds: the [V.sub.max] limit of 42 mph, 51 mph, and 60 mph.

These results, and all the other results, show that the C0 design resulted in a significant improvement over both the AREMA straight and curved switch point designs. Furthermore, the C0 design produced results that were nearly as good as those of the tangential geometry design. However, the C0 results were attained without the additional 20 feet of turnout lead length required by the tangential geometry turnout.

Implementation

The simulation results demonstrated that superior vehicle performance was achieved by a design with a very-low entry angle and uniform curvature. Vehicle behavior at 51 mph over this turnout configuration was significantly better than over the AREMA straight point design at its speed limit of 36 mph, and the AREMA curved point design at its limit of 51 mph. In addition, the new design performed almost as well as the tangential geometry turnout, without the additional 20-foot lead length. Finally, the results over the new design showed improved performance at speeds as high as 60 mph, without exceeding any established safety limits (limits on L/V ratios, lateral acceleration, wheel unloading, etc.).

Based on the results of this analysis, FRA authorized Phase II of this project with the purpose of fabricating, installing and testing one of the new optimized turnout geometries (C0). Two prototype No. 20 turnouts were designed in conjunction with, and manufactured by, Cleveland Track Material, Inc., and contributed to New Jersey Transit as part of this study. These turnouts are currently being installed on the Ridgewood, N.J., crossover by New Jersey Transit.

Testing of the two turnouts is scheduled for late-Summer 2004. This testing will include comprehensive measurements of the performance of the new design turnout, as compared to a standard AREMA turnout. Behavioral assessment will be based on measurements of lateral and vertical forces and/or accelerations at strategic locations in the turnout.

Based on results to date, the new turnout designs appear to offer a low-cost means to increase the speeds through existing turnouts. By establishing a superior geometry within the same dimensions as the AREMA standard, improved performance is achieved without the need of additional space and without the high cost of relocating the frog or switch. In addition, it is expected that the optimized geometry will result in improved ride quality and decreased wear, thus leading to a longer service life and decreased maintenance costs.