Superelevation Position. Figure 2.9 shows the recommended positioning of the
proposed superelevation transition in relationship to the horizontal curve. For those
curves with spirals, the transition from adverse crown removal to full superelevation
should occur within the limits of the spiral. In other words, the spiral length should
equal the L value, usually rounded to the nearest 25 ft (7.6 m).
For simple curves without spirals, the L transition should be placed so that 50 to
70 percent of the maximum superelevation rate is outside the curve limits (point of
curvature PC to point of tangency PT). It is recommended that whenever possible,
two-thirds of the full superelevation rate be present at the PC and PT. See the case
diagrams in Fig. 2.9 for a graphic presentation of the recommended positioning.