Technology Digests / Vehicle-Induced Longitudinal Rail Forces in High-Grade Environments

TD23-012

July 25, 2023
Authors
  • Stephen Wilk
  • Dustin Clasby
  • Yin Gao
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Key Findings

  • Rail temperature measurements at a revenue service site showed that sustained braking on a 1.8 percent grade with a 9.25-degree curve increased rail temperatures up to a measured maximum of 26°F during train passage, but commonly only reached an increase of 15°F. Influential factors were direction (uphill traction versus downhill sustained air braking), the number of axles, and the average axle load.
  • Rail temperatures decreased non-linearly after train passage and often did not fully cool before the next train pass (residual rail temperatures). Increased rail temperatures could accumulate and produce higher rail temperatures than would be created from a single train pass.
  • Worst-case rail temperatures can be conservatively estimated by adding 1) ambient temperature above RNT, 2) solar radiation (+30°F), 3) rail temperature increase from train braking, and 4) residual heat from previous train passes. Operating rules (e.g., spacing out heavy downhill trains on very hot, sunny days) can be implemented to significantly reduce high-risk situations.

Vehicle-Induced Longitudinal Rail Forces in High-Grade Environments

MxV Rail measured and analyzed multiple vehicle-induced thermal and mechanical longitudinal rail forces in a high-grade revenue service environment. Though difficult to measure, longitudinal rail force is the main factor that produces track buckles, making in-field estimates of longitudinal rail forces important for track buckle risk mitigation. MxV Rail’s analysis focused on measuring vehicle-induced longitudinal rail forces and estimating ranges anticipated in various revenue service track and operating environments. This work is supported by the Association of American Railroads (AAR) under its Strategic Research Initiatives (SRI) program.   LONGITUDINAL RAIL FORCES  Longitudinal rail forces develop when the rail temperature reaches a point above (compressive) or below (tensile) the rail neutral temperature (RNT). It is well established that ambient (air) temperatures and solar radiation are key for estimating rail temperatures. On hot, sunny, non-windy days, the rail temperature can be 30°F hotter than the ambient temperature.1 Vehicles can also affect longitudinal rail…