### Appendix D Alignment and Superelevation

The central angle of a spiral (∆s) is a function of the average degree of curvature of the spiral. In other words, ∆s of a spiral is one half of the central angle (∆ C) for a circular curve of the same length and degree of curvature. Since then Spiral components such as X, Y, T, Q, ST, and LT are routinely found in spiral curve tables.

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