Wisconsin DOTWisconsin DOTFacilities Development Manual Facilities Development Manual
(FDM)(FDM)
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Weston PhilipsWeston Philips1/27/051/27/05
SuperelevationSuperelevation
Vertical Vertical AlignmentAlignment
SuperelevationSuperelevation
Ch. 3 Elements of Design
In Horizontal Alignment Section
p. 173
Ch. 2 Alignments
Section 2A-2, 2A-3
A different angle on A different angle on superelevation?superelevation?
Axis of RotationAxis of Rotation
1.1. Rotate pavement about Rotate pavement about centerlinecenterline
2.2. Rotate about Rotate about inner edgeinner edge of pavement of pavement
3.3. Rotate about Rotate about outside edgeoutside edge of pavement of pavement
4.4. Rotate about center of Rotate about center of medianmedian (Divided) (Divided)
Axis of RotationAxis of Rotation
Axis of RotationAxis of Rotation
Superelevation ProfileSuperelevation ProfileTwo-Lane Highway – Centerline RotationTwo-Lane Highway – Centerline Rotation
Normal CrownNormal Crown
Tangent Runout/Crown Tangent Runout/Crown RunoffRunoff
Horizontal
Superelevation RunoffSuperelevation RunoffSuperelevation = Cross SlopeSuperelevation = Cross Slope
Superelevation AchievedSuperelevation Achieved
Max Superelevation RateMax Superelevation Rate
Nomograph (Discussed Later)
Max Superelevation Rate Max Superelevation Rate Cont’dCont’d
How to Calculate How to Calculate SuperelevationSuperelevation
1.1. Using Superelevation TablesUsing Superelevation Tables
2.2. NomographsNomographs
3.3. Simple Curve FormulaSimple Curve Formula
Superelevation Option 1Superelevation Option 1
► First solution is obtained from the superelevation tables, emax = 0.04 (Figure 9)
► R = 700.; e = 0.039
Given: VD = 40 mphR = 700 ft.fmax = 0.178 (from Table 7)
3.9%3.9%
Note: Choose Note: Choose Table emax = Table emax =
0.040.04
Iowa has ramp tables.
Minimum RadiusMinimum Radius
► Greenbook p. 145 (186 pdf)Greenbook p. 145 (186 pdf) Minimum Radius TableMinimum Radius Table
Superelevation Option 2Superelevation Option 2
Radius
40mph
700 feet
e = -2.5%
Note: Greenbook contains derivation of equations/graphs.
Superelevation Option 3Superelevation Option 3
Third solution is obtained from the simplified curve formula:
e = (VD2/15R) - fmax (English version)
e = (402/15*700) - 0.178 = 0.152 - 0.178 = -0.0256-2.56%
Where:VD = design speedR = radiuse = superelevation ratefmax= maximum side friction.
Note: Metric Versione = (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 PlacementTransition 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.
CalculationsCalculations
Given:PC = Station 870+00.00L = 115 ft. (Table 7, 40mph design
speed)X = L * NC/ e = 115 * .02/.02 = 115ft
Theoretical point of normal crownPC - 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 CurvatureL = Length of RunoffX = Length of Tangent RunoutNC = Normal Crown of 2%
Length of Runoff (L)Length of Runoff (L)
The adjustment factor (α) is used to adjust for different roadway widths.
Length of Runoff (L)Length of Runoff (L)
►Greenbook p. 171 (pdf 212)Greenbook p. 171 (pdf 212)
Length of Runoff (L)Length of Runoff (L)
Tangent Runout LTangent Runout Ltt or X or X
Tangent Runout LTangent Runout Ltt or X or X
Tangent Runout LTangent Runout Ltt or X or X
Tangent Runout LTangent Runout Ltt or X or X
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Vertical AlignmentVertical 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.
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No Vertical Curves?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 Max % Grade By Functional ClassClass
Vertical CurvesVertical Curves
Vertical curves are generallyidentified 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:Question:
Is there more on Vertical Is there more on Vertical Alignment in the Wisconsin Alignment in the Wisconsin
Manual?Manual?
2A-1
p. 235 (276 pdf)
