Technology Digests / Stock Rail Undercut Flow Evaluation Test

TD26-017

Date Posted: August 5, 2026
Authors
  • Ekrem Koç
  • Duane Otter
  • Beatrice Rael
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Key Findings

  • For the two routes studied, the railroads are appropriately controlling the amounts of stock rail flow on the respective lines. On one line, the switches are ground annually before the flow reaches an amount that could cause switch point chipping or gapping. On the other line, the amount of flow is so low that grinding has not been needed for a few years.
  • Stock rail flow development was highly localized, with any measurable undercut flow tending to occur primarily within the first ~3 feet from the Point of Switch (POS).
  • Site-specific conditions, including traffic characteristics, diverging route usage, wheel populations, and local maintenance constraints, may have a greater influence on undercut flow accumulation than specialty grinding practices.
  • At the test site with no specialty turnout grinding, the measured flow was comparable to or lower than pre-grind (worst-case) conditions at the annually ground sites, likely due to differences in the train operations over each line.

Stock Rail Undercut Flow Evaluation Test

Rail flow at the switch point/stock rail interface can prevent proper closure of the switch and lead to switch point chipping, thereby requiring frequent grinding and increased maintenance efforts. To address this challenge, MxV Rail conducted a revenue service test between 2021 and 2023 to evaluate how rail flow develops at the switch point/stock rail interface under different maintenance practices. The objectives of this testing, conducted under the Association of American Railroads’ (AAR) Strategic Research Initiatives (SRI) program, were to 1) quantify in-service stock rail undercut flow, 2) determine the influence of grinding practices, and 3) explore opportunities to optimize turnout maintenance and design. In cooperation with Norfolk Southern Railway (NS) and Union Pacific Railroad (UP), MxV Rail engineers conducted field measurements on switches in two different environments: one that receives annual specialty grinding and one that does not. The highlights of the field measurement procedures and findings of the…