Interface - The Journal of Wheel/Rail Interaction

CURVE SUPERELEVATION

Curve Superelevation: Problems and Solutions
By Gary Wolf • January, 2006

Railroad engineering managers have been struggling with the problem of how much elevation to place in a curve since the first steam engines started turning a wheel. While the physics and calculus of the matter seem straightforward, the application of those formulas is where problems arise. The classic formulas used by the Federal Railroad Administration (FRA) and others to determine correct superelevation contain two variables: the degree of curvature and the speed of the train.

Thus, the correct amount of superelevation to balance the train’s centrifugal forces is:

It looks like a simple matter of plugging in the numbers and calculating the answer. But it’s not a simple matter. While the degree of curvature is generally fixed, the correct speed to use causes much confusion. There are several recurring scenarios that can create problems.

Most difficult, perhaps, is dealing with the problems associated with heavy grade territory, where uphill trains may struggle to maintain the minimum continuous speed of 12 mph, while downhill trains can round the curves at the timetable speed of 35 mph. Which speed do you use in the formula?

A second recurring problem is accommodating both freight and passenger trains in the same corridor. The tonnage-laden freight might struggle to make 40 mph, while the sleek and horsepower-heavy Amtrak train can move along at 79 mph. Which speed do you use in the formula?

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