superelevation 1
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Wisconsin DOTFacilities Development Manual (FDM)http://www.dot.ca.gov/dist1/d1traffic/cap/curve.jpgWeston Philips1/27/05
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Superelevation
Vertical Alignment
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Superelevation
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A different angle on superelevation?Ch. 3 Elements of DesignIn Horizontal Alignment Sectionp. 173Ch. 2 AlignmentsSection 2A-2, 2A-3
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Axis of RotationRotate pavement about centerline Rotate about inner edge of pavement Rotate about outside edge of pavementRotate about center of median (Divided)
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Axis of Rotation
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Axis of Rotation
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Superelevation ProfileTwo-Lane Highway Centerline Rotation
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Normal Crown
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Tangent Runout/Crown RunoffHorizontal
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Superelevation RunoffSuperelevation = Cross Slope
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Superelevation Achieved
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Max Superelevation RateNomograph (Discussed Later)
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Max Superelevation Rate Contd
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How to Calculate SuperelevationUsing Superelevation Tables
Nomographs
Simple Curve Formula
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Superelevation Option 1First 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%Note: Choose Table emax = 0.04
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Iowa has ramp tables.
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Minimum RadiusGreenbook p. 145 (186 pdf)Minimum Radius Table
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Superelevation Option 2Radius40mph700 feete = -2.5%
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Note: Greenbook contains derivation of equations/graphs.
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Superelevation Option 3Third 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).
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Superelevation TransitionSuperelevation transition is the length required to rotate the cross slope of a highway from a normal crowned slope to a fully superelevated cross slope.
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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.
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CalculationsGiven: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%
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Length of Runoff (L)
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The adjustment factor () is used to adjust for different roadway widths.Length of Runoff (L)
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Greenbook p. 171 (pdf 212)Length of Runoff (L)
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Tangent Runout Lt or X
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Tangent Runout Lt or X
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Tangent Runout Lt or X
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Tangent Runout Lt or X
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http://www.scvresources.com/highways/sr_23.htmVertical Alignment
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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
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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.
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Max % Grade By Functional Class
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Vertical CurvesVertical 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
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Question:
Is there more on Vertical Alignment in the Wisconsin Manual?2A-1p. 235 (276 pdf)