Curve Superelevation: Problems and Solutions (continued)
FRA definitions
The FRA track safety standards (TSS) Section 213.57 defines maximum allowable curve speeds based on allowing up to a 3-inch unbalance (see Figure 4). Appendix A, of Section 213 provides charts defining maximum allowable speeds for various degrees of curvature and superelevation. While there are penalties for over-speed operation, there is no prohibition against operating a train at a speed lower than the timetable speed, despite the danger this presents.
Theory of Under Balance
The Newtonian physics of calculating a suitable superelevation can be seen in Figure 5. A suitable elevation can be determined based on the centrifugal force developed at a given speed, the height of center of gravity of the equipment and the gauge of the track. Following the formula for a 4-degree curve and a timetable speed of 30 mph, assuming the use of equipment with average CG heights and nominal 56-1/2-inch gauge track, a roadmaster will presumably put 2.4 inches of elevation in the curve. During his inspection trips, he may start to notice the development of a series of undesirable conditions:
• The low rail starts spalling.
• Differential plate cutting causes the low rail to cant to the filed side.
• The curve starts to gain elevation over a year cycle.
If he checks his calculations, he’ll find that he did them correctly. So what went wrong? The equations didn’t reflect the reality of the situation. The timetable speed was correctly listed as 30 mph, but few, if any, trains live up to this expectation. In the real world of railroad operations, speed is a variable, and many trains operate at less than the timetable speed for a variety of reasons:
• Locomotives fail to develop full horsepower.
• Slow orders placed on the track.
• Train running at restricted speed due to signal or warrant control.
OCTOBER 2005 "Operating at High Cant Deficiency" READ ARTICLE
FEBRUARY 2005 "Rock 'til you Drop: Starting and Stopping Harmonic Rock and Roll" READ ARTICLE
AUGUST 2004 "Effects of Rail Cant on Wheel/Rail Forces and Derailment Potential" READ ARTICLE
MARCH 2005 "Preventing Track Buckles" READ ARTICLE
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The FRA track safety standards (TSS) Section 213.57 defines maximum allowable curve speeds based on allowing up to a 3-inch unbalance (see Figure 4). Appendix A, of Section 213 provides charts defining maximum allowable speeds for various degrees of curvature and superelevation. While there are penalties for over-speed operation, there is no prohibition against operating a train at a speed lower than the timetable speed, despite the danger this presents.
The Newtonian physics of calculating a suitable superelevation can be seen in Figure 5. A suitable elevation can be determined based on the centrifugal force developed at a given speed, the height of center of gravity of the equipment and the gauge of the track. Following the formula for a 4-degree curve and a timetable speed of 30 mph, assuming the use of equipment with average CG heights and nominal 56-1/2-inch gauge track, a roadmaster will presumably put 2.4 inches of elevation in the curve. During his inspection trips, he may start to notice the development of a series of undesirable conditions:
