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6. Five- or ten-chord spiral

It is common to compute (and stake) a spiral in equal intervals rather than full- or half-stations. Depending on spiral length and arc degree of curvature, the spiral is computed in either five or ten equal intervals. For example, a 200 foot five-chord spiral would be computed at a 40 foot interval.

Although this results in spiral points with odd stations, its advantage is a single set of calculations for the entrance and exit spirals. Because the deflection angle method is computed from a spiral's flat end, TS for the entrance and ST for the exit, the same equal interval computations can be used for both. We'll see this in the following example.

 

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