Technology Digests / Longitudinal Rail Forces from Locomotive Traction

TD25-017

September 23, 2025
Authors
  • Yi Wang
  • Stephen Wilk
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Key Findings

  • The longitudinal rail force (LRF) in each rail at a location three ties ahead of the leading axle of a train movement can be approximated as 10 percent of the traction forces produced by the leading locomotive.
  • The relationship between the traction forces of a shoving distributed power locomotive consist at the rear of the train and the measured LRF behind the last powered axle was inconclusive, requiring further testing and verification.
  • The measured LRF as a percentage of the traction forces appeared to have lower magnitude and less variation on tangent track compared to curved track.

Longitudinal Rail Forces from Locomotive Traction

Under the Association of American Railroads (AAR) Strategic Research Initiative program, MxV Rail measured the longitudinal rail force (LRF) resulting from traction forces generated by locomotives at the Facility for Accelerated Service Testing (FAST®). Performed as part of MxV Rail’s ongoing work to better understand vehicle effects on track stability, the tests provided validations to similar measurements previously taken in the revenue service environment.1,2 Background The stress state of continuously welded rail changes as the rail steel experiences thermal expansion and contraction. The LRF develops as the temperature of the rail changes from its rail neutral temperature (RNT). The rail is in tension when the temperature is below the RNT and in compression when the temperature is above the RNT. A significant portion of the longitudinal forces exerted on the rail from the vehicle or other external factors are transferred to fasteners, ties, and the substructure, all of which provide…