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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Very Long Trains – Phase II - Rack Tests

Document Series
Technical Reports
Federal Railroad Administration
Report Number
Subject Rolling Stock
Very Long Train, VLT, Air Brake System, Distributed Power

In Phase II of this research project, FRA sponsored Wabtec to perform train air brake tests on long trains at their facility in Wilmerding, Pennsylvania, between January 2021 and March 2021. The air brake rack simulated trains with up to 200 control valves using a conventional (i.e., head-end power only) configuration. Test results, summarized by Wabtec in a separate report, were shared with Sharma & Associates, Inc. (SA), who performed detailed analysis from June 2021 to November 2021 at its office in Countryside, Illinois, to understand the issues of brake signal propagation, brake pipe pressure reduction, brake cylinder (BC) pressure buildup, and false gradient braking on VLTs. The data analysis revealed that there were slightly slower response times and slightly reduced brake cylinder pressures as the train length increased, with leakage levels further contributing to the differences. When subsequent brake applications were made without waiting for the brake pipe pressure at the rear of the train to fully recover, the likelihood of unintended brake releases were higher with longer trains. Such situations can be avoided by making the second application appropriately deeper than the first application.

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Last updated: Monday, June 3, 2024