Superelevation 1

Wisconsin DOTFacilities Development Manual (FDM)http://www.dot.ca.gov/dist1/d1traffic/cap/curve.jpgWeston Philips1/27/05

Superelevation

Vertical Alignment

Superelevation

A different angle on superelevation?Ch. 3 Elements of DesignIn Horizontal Alignment Sectionp. 173Ch. 2 AlignmentsSection 2A-2, 2A-3

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

Axis of Rotation

Superelevation ProfileTwo-Lane Highway Centerline Rotation

Normal Crown

Tangent Runout/Crown RunoffHorizontal

Superelevation RunoffSuperelevation = Cross Slope

Superelevation Achieved

Max Superelevation RateNomograph (Discussed Later)

Max Superelevation Rate Contd

How to Calculate SuperelevationUsing Superelevation Tables

Nomographs

Simple Curve Formula

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

Iowa has ramp tables.

Minimum RadiusGreenbook p. 145 (186 pdf)Minimum Radius Table

Superelevation Option 2Radius40mph700 feete = -2.5%

Note: Greenbook contains derivation of equations/graphs.

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).

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.

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.

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%

Length of Runoff (L)

The adjustment factor () is used to adjust for different roadway widths.Length of Runoff (L)

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

Tangent Runout Lt or X

http://www.scvresources.com/highways/sr_23.htmVertical 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.

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 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

Question:

Is there more on Vertical Alignment in the Wisconsin Manual?2A-1p. 235 (276 pdf)

Documents

Superelevation 1