The job of designing spirals is one for qualified engineers. In general, however, the length of spirals
depends upon the amount of superelevation of the circular curve and, to an extent, on the general train speed.
These relationships are tabulated in table V. Spiral design depends on the amount of increase in superelevation to
which a train is subjected per second. Therefore, trains which approach the curve at a high rate of speed require
long spirals. Similarly, a curve with less superelevation needs a shorter spiral than a curve with greater
Table V. Spiral Lengths on Curves for Various Elevations and Speeds
In a theater, time is usually all important, and constructing proper spirals takes a great deal of time.
Therefore, the Corps of Engineers has specified that railway curves of 2 degrees or less