22 Note: Greenbook contains derivation of equations/graphs.
23 Superelevation Option 3 Third solution is obtained from the simplified curve formula:e = (VD2/15R) - fmax (English version)e = (402/15*700) = =-2.56%Where:VD = design speedR = radiuse = superelevation ratefmax= maximum side friction.Note: Metric Versione = (VD2/127R) - fmax (metric version).
24 Superelevation Transition Superelevation transition is the length required to rotate the cross slope of a highway from a normal crowned slope to a fully superelevated cross slope.
25 Transition PlacementWisDOT practice is to place the tangent runout and approximately two-thirds of the length of runoff on the tangent approach and one-third of the length of runoff on the curve.
26 CalculationsCompute the theoretical point of normal crown and the theoretical point of full superelevation.Given:PC = StationL = 115 ft. (Table 7, 40mph design speed)X = L * NC/ e = 115 * .02/.02 = 115ftTheoretical point of normal crownPC - 2/3L - X = =StationTheoretical point of full superelevationPC + 1/3L = =StationWhere:PC = Point of CurvatureL = Length of RunoffX = Length of Tangent RunoutNC = Normal Crown of 2%
36 The highway vertical alignment consists of tangents or grades and vertical curves. Design vertical curves to provide adequate sight distance, safety, comfortable driving, good drainage, and pleasing appearance.
37 No Vertical Curves?“Although grade changes without a vertical curve are discouraged, there may be situations where it is necessary.”“Some rounding of the deflection point is anticipated during construction.”
39 K Vertical Curves Vertical curves are generally identified by their K values.K is the rate of curvature and is defined as the length of the vertical curve divided by the algebraic difference in gradeNote: For Drainage, use K > 167K
40 Question: Is there more on Vertical Alignment in the Wisconsin Manual? p. 235 (276 pdf)
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