Technology Digests / Performance Considerations for Automatic Secondary Securement Devices

TD26-007

May 21, 2026
Authors
  • Yi Wang
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Key Findings

  • The emergency vent rate of the brake pipe (BP) dictates the minimum time delay required to allow full brake force development. Due to the fast rate of emergency venting, ASSD locking threshold pressures over the evaluated range of 5 to 10 psi do not cause significant variance in the required locking delay.
  • The baseline brake performance dictates the effectiveness of the ASSD. For example, under normal circumstances with brakes applied after a fully charged BP, at least half of the cars need to be equipped with an ASSD for the effective securement of a uniform loaded bulk commodity train on a 2 percent grade.
  • A high ASSD unlocking threshold pressure (e.g., 60 psi) can result in a significant delay in brake release, and the effects of this delay should be analyzed carefully as part of any ASSD performance standardization. A lower unlocking threshold pressure (40 psi for example) would result in minimum change from current operating scenarios.

Performance Considerations for Automatic Secondary Securement Devices

Under the Association of American Railroads (AAR) Strategic Research Initiative (SRI) program, MxV Rail is testing automatic secondary securement devices (ASSDs) from several manufacturers to help the AAR Brake Systems Committee evaluate the performance of these devices. Because ASSDs do not have a usage history in the North American market, results of this research may also help the committee determine the relevant standards in interchange service. While testing is ongoing, MxV Rail has also modeled different performance envelopes, the results of which are presented in this Technology Digest. The goal of the modeling is to assess the effect of selecting different performance targets for ASSD function and train operation. BACKGROUND Train operators typically use handbrakes to secure freight equipment, especially on grades, when unattended, or over a long period of time.1 Unlike pneumatic brakes, handbrakes engage the brake shoes and wheels mechanically rather than relying on brake cylinder pressure (BCP).…