Note: Greenbook contains derivation of equations/graphs.
Superelevation Option 3 Third solution is obtained from the simplified curve formula: e = (VD 2 /15R) - f max (English version) e = (40 2 /15*700) - 0.178 = 0.152 - 0.178 = -0.0256 -2.56% Where: VD = design speed R = radius e = superelevation rate f max = maximum side friction. Note: Metric Version e = (VD 2 /127R) - f max (metric version).
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.
Transition Placement ► ► WisDOT 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.
Calculations Given: PC = Station 870+00.00 L = 115 ft. (Table 7, 40mph design speed) X = L * NC/ e = 115 *.02/.02 = 115ft Theoretical point of normal crown PC - 2/3L - X = 870+00.00 - 76.67 - 115 = Station 868+08.33 Theoretical point of full superelevation PC + 1/3L = 870+00.00 + 38.33 = Station 870+38.33 ► Compute the theoretical point of normal crown and the theoretical point of full superelevation. Where: PC = Point of Curvature L = Length of Runoff X = Length of Tangent Runout NC = Normal Crown of 2%
Length of Runoff (L)
The adjustment factor (α) is used to adjust for different roadway widths. Length of Runoff (L)
► Greenbook p. 171 (pdf 212) Length of Runoff (L)
► ► 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. http://listproc.ucdavis.edu/archives/cbximages/log0306/att-0011/01-CoolRide.jpg
No Vertical Curves? “Some rounding of the deflection point is anticipated during construction.” “Although grade changes without a vertical curve are discouraged, there may be situations where it is necessary.”
Max % Grade By Functional Class
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 grade Note: For Drainage, use K > 167 K
Question: Is there more on Vertical Alignment in the Wisconsin Manual? 2A-1 p. 235 (276 pdf)