Super Elevation

transcript

Wisconsin DOTWisconsin DOTFacilities Development Manual Facilities Development Manual

(FDM)(FDM)

http://www.dot.ca.gov/dist1/d1traffic/cap/curve.jpghttp://www.dot.ca.gov/dist1/d1traffic/cap/curve.jpg

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

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

Radius

700 feet

e = -2.5%

Note: Greenbook contains derivation of equations/graphs.

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.

►Greenbook p. 171 (pdf 212)Greenbook p. 171 (pdf 212)

Tangent Runout LTangent Runout Ltt or X or X

http://www.scvresources.com/highways/sr_23.htmhttp://www.scvresources.com/highways/sr_23.htm

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

Question:Question:

Is there more on Vertical Is there more on Vertical Alignment in the Wisconsin Alignment in the Wisconsin

Manual?Manual?

p. 235 (276 pdf)

Super Elevation

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