A spiral is a mathematically defined curve with a changing radius that varies in proportion to the length of the curve.
Accessed via the Configure Alignment command, the system can be set to use either a Clothoid or Cubic Parabola type spiral.
Clothoid
At any point on a clothoid type spiral, the product of its radius at that point and its length to that point
is a constant value. It is also commonly known as a Transition, Eulers, or Glovers spiral. Clothoids are typically
used in Road Design.
Cubic Parabola
Typically found in Railway design, Cubic parabolas are defined as per the Australian NSW RailCorp definition for Transition curves as
per document ESC 210, titled RailCorp Infrastructure Engineering Standard - Track, Track Geometry and Stability Version 4.0. The main difference between a clothoid
and a cubic parabola is that a cubic parabola is restricted in the maximum length the spiral can be, that being 0.68 *
the end radius of the spiral.
A cubic parabola spiral also differs from a clothoid by the rate of change of the radius with varying length.
Spirals in a data base file have all the attributes of Lines. These attributes may be set in the Attributes/Line command located in the Computations task.