Technical Reports

Effect of Track Twist on Vehicle Dynamic Performance

  • 13
  • Mar
  • 1997
AUTHOR: Association of American Railroads
KEYWORDS: Track Twist, Track Geometry, Wheel/Rail Friction
ABSTRACT: Results of tests conducted at the Transportation Technology Center (TTC), Pueblo, Colorado, indicate that vehicle response to track twist varies significantly with car type. Critical response variables include car body torsional stiffness, truck spacing, track alignment (tangent or curve), track geometry and wheel/rail friction coefficient. Test data collected during this project provides an experimental basis for investigation of performance-based track safety limits. Track twist is defined as a variation in cross level between two points along the track. Excessive twist can cause true center plate unloading on tangent track as indicated by wheel unloading, or wheel climb on curved-track as indicated by high wheel or axle LN ratios. The limiting wheel unloading and LN ratio criteria specified by the industry for new car acceptance (90 percent reduction of static vertical wheel force, 1.0 single wheel LN ratio and 1.5 axle sum LN ratio) were used as the guideline limits for this test. Three vehicles were tested in an empty load condition- a 100-ton, 89-foot center beam flatcar, a 100-ton covered hopper car and a 70-ton tank car- over cross level and combined cross level/alignment perturbations on tangent, 7.5- degree curve, and 12-degree curve test zones.