Interface - The Journal of Wheel/Rail Interaction

EFFECTS OF WIDE GAUGE

Effects of Wide Gauge on Derailment Potential (Part 1 of 2)
By Gary P. Wolf • December 1, 2004

"Wide gauge" is one of the most often used FRA derailment codes. In 2003, 254 derailments were reported to have been caused by wide gauge (FRA code T110 or T111). This represents nearly 13% of all derailments reported to the FRA, and roughly 30% of all track-related derailments. With such a significant number of derailments attributed to it, all eyes should be trained on identifying wide gauge before a derailment occurs.

The question is: Are "wide gauge" derailment conditions simply a track problem? Or can the root cause of a wide gauge derailment actually have a mechanical origin?

Gauge is nominally set at 56 1/2 inches in North America. As wheelsets roll through a curve, the wheels on both the high and low rails produce an outward, lateral, gauge-spreading force. Track with timber ties and cut spike fasteners is fairly elastic under lateral forces of approximately 20,000 pounds or less. That is, the gauge might spread slightly, but after the train passes, the gauge snaps back to its original dimension. However, when lateral, gauge-spreading forces exceed 20,000 pounds, permanent deformation of the ties and fastening system can occur. That is, the gauge no longer snaps back to its original dimension, but stays in a wider position than originally set.

On a microscopic basis, wood fibers around the spike are compressed and deformed slightly. The spike itself might bend. In total, the gauge is incrementally and permanently widened from its initial position by the repetitive application of lateral wheel loads. And those few wheelsets producing the highest lateral loads have the potential to do the most and permanent damage. Eventually, the spike holes become elongated to the point where the spikes are loose, and often work themselves up out of the spike hole. (Figure 1 shows an example of elongated spike holes.)

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