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Brad Kerchof

Brad Kerchof
Norfolk Southern Railway


Effects of Superelevation and Speed on Vehicle Curving

Theoretical studies and tests at TTCI have shown that:

  • Heavy trains curving with excessive elevation generally impose high vertical loads on the low rail and high steering tractions on the lead axle of the truck leading to low rail rolling contact fatigue and high gage spread forces.
  • Trains curving at an elevation deficiency impose higher vertical loads on the high rail, however trucks curve with a reduced angle of attack and generate lower lead axle steering tractions with resulting lower L/V ratios.

To see whether these theories could be validated in revenue service, TTCI and NS established a vertical and lateral force measurement site in Maybeury, WV, on a segment of track that included three consecutive 4.5′ curves with 3.5″ elevation. A 1.22% ascending grade insured that the unit coal trains operated at maximum throttle, typically at speeds of between 11 and 13 mph, significantly below balance speed of 33 mph. This work established the base condition, and was termed Phase 1.

Under phase 2, the elevation on all three curves was reduced to 1 inch (resulting in a balance speed of 17 mph), and a similar set of force measurements were taken.

The results validated the theoretical conclusions:

  • The difference between high and low rail vertical loads was reduced, and the maximum vertical force on the low rail was reduced.
  • Gage-spreading forces were reduced.
  • High rail L/V ratio was reduced.
  • Speed increased slightly.

This paper will describe both phases of this revenue service test.