Super Elevation

Wisconsin DOT Facilities Development Manual (FDM)

Weston Philips 1/27/05 http://www.dot.ca.gov/dist1/d1traffic/cap/curve.jpg

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Superelevation

 Vertical

Alignment 

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Superelevation

 Vertical

Alignment 

Superelevation

 A different angle on superelevation?

Ch. 3 Elements of Design

In Horizontal Alignment Section

Ch. 2 Alignments

p. 173

Section 2A-2, 2A-3

 Axis of Rotation 1. Rotate pavement about centerline 2. Rotate about inner 3. 4.

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  Two  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 1.

Using Superelevation Tables

2.

Nomographs

3.

Simple Curve Formula

Superelevation Option 1 Given: VD = 40 mph R = 700 ft. fmax = 0.178 (from Table 7)

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First solution is obtained from the superelevation tables, emax = 0.04 (Figure 9) R = 700.; e = 0.039

Note: Choose

Table emax = 0.04

3.9%

Iowa has ramp tables.

Minimum Radius 

Greenbook p. 145 (186 pdf) 

Minimum Radius Table

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) - f max (English version) e = (402 /15*700) - 0.178 = 0.152 - 0.178 = -0.0256 -2.56% Where:  VD = design speed R = radius e = superelevation rate f max= maximum side friction. Note: Metric Version e = (VD2 /127R) - f max (metric version).

Superelevation

Transition

uperelevation 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 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 870+00.00 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 = 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

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)

The adjustment factor () is used to adjust for different roadway widths.

Length of Runoff (L)

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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 

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

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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.

htt ://list roc.ucdavis.edu/archives/cbxima es/lo 0306/att-0011/01 0306/att 0011/01-CoolRide.

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

 Vertical Curves  Vertical curves are generally identified by their K values.

K

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