# Wisconsin DOT Facilities Development Manual (FDM)

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Wisconsin DOT Facilities Development Manual (FDM)
Weston Philips 1/27/05

Superelevation Vertical Alignment

Superelevation

A different angle on superelevation?
Ch. 3 Elements of Design In Horizontal Alignment Section p. 173 Ch. 2 Alignments Section 2A-2, 2A-3

Axis of Rotation Rotate pavement about centerline
Rotate about inner edge of pavement Rotate about outside edge of pavement Rotate about center of median (Divided)

Axis of Rotation

Axis of Rotation

Superelevation Profile
Two-Lane Highway – Centerline Rotation

Normal Crown

Tangent Runout/Crown Runoff
Horizontal

Superelevation Runoff
Superelevation = Cross Slope

Superelevation Achieved

Max Superelevation Rate
Nomograph (Discussed Later)

Max Superelevation Rate Cont’d

How to Calculate Superelevation
Using Superelevation Tables Nomographs Simple Curve Formula

Superelevation Option 1
Given: VD = 40 mph R = 700 ft. fmax = (from Table 7) First solution is obtained from the superelevation tables, emax = 0.04 (Figure 9) R = 700.; e = 0.039 3.9% Note: Choose Table emax = 0.04

Iowa has ramp tables.

Superelevation Option 2
Radius 700 feet e = -2.5% 40mph

Note: Greenbook contains derivation of equations/graphs.

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 speed R = radius e = superelevation rate fmax= maximum side friction. Note: Metric Version e = (VD2/127R) - fmax (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 Compute the theoretical point of normal crown and the theoretical point of full superelevation. Given: PC = Station 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 = = Station Theoretical point of full superelevation PC + 1/3L = = Station Where: PC = Point of Curvature L = Length of Runoff X = Length of Tangent Runout NC = Normal Crown of 2%

Length of Runoff (L)

Length of Runoff (L) Greenbook p. 171 (pdf 212)

Tangent Runout Lt or X

Tangent Runout Lt or X

Tangent Runout Lt or X

Tangent Runout Lt or X

Vertical Alignment

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.

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.”

Max % Grade By Functional Class

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 grade Note: For Drainage, use K > 167 K

Question: Is there more on Vertical Alignment in the Wisconsin Manual?
p. 235 (276 pdf)