Superelevation Guidlines

8/12/2019 Superelevation Guidlines

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WSDOT Design Manual M 22-01.05 Page 1250-1June 2009

Chapter 1250 Superelevation

1250.01 General1250.02 References1250.03 De nitions1250.04 Superelevation Rate Selection1250.05 Existing Curves1250.06 Turning Movements at Intersections1250.07 Runoff for Highway Curves1250.08 Runoff for Ramp Curves1250.09 Documentation

1250.01 GeneralTo maintain the design speed, highway and ramp curves are usually superelevatedto overcome part of the centrifugal force that acts on a vehicle.

For additional information, see the following chapters:

Chapter Subject 1130 Roadway widths and cross slopes for modi ed design level

1140 Minimum lane and shoulder widths for full design level 1360 Lane and shoulder widths for ramps

1250.02 References

(1) Design Guidance

Standard Plans for Road, Bridge, and Municipal Construction ( Standard Plans ),M 21-01, WSDOT

Standard Speci cations for Road, Bridge, and Municipal Construction( Standard Speci cation s ), M 41-10, WSDOT

(2) Supporting Information

A Policy on Geometric Design of Highways and Streets (Green Book),AASHTO, 2004

1250.03 De nitionslane A strip of roadway used for a single line of vehicles.

lane width The lateral design width for a single lane, striped as shown in the

Standard Plans an d the Standard Speci cation s.median The portion of a highway separating the traveled ways for traf c inopposite directions.

roadway The portion of a highway, including shoulders, for vehicular use.
http://1130.pdf/http://1130.pdf/http://1140.pdf/http://1140.pdf/http://1360.pdf/http://1360.pdf/http://www.wsdot.wa.gov/Publications/Manuals/M55-05.htmhttp://www.wsdot.wa.gov/Publications/Manuals/M55-05.htmhttp://www.wsdot.wa.gov/Publications/Manuals/M55-05.htmhttp://www.wsdot.wa.gov/Publications/Manuals/M55-05.htmhttp://www.wsdot.wa.gov/Publications/Manuals/M41-10.htmhttp://www.wsdot.wa.gov/Publications/Manuals/M41-10.htmhttp://www.wsdot.wa.gov/Publications/Manuals/M41-10.htmhttp://www.wsdot.wa.gov/Publications/Manuals/M41-10.htmhttp://www.wsdot.wa.gov/Publications/Manuals/M41-10.htmhttp://www.wsdot.wa.gov/Publications/Manuals/M55-05.htmhttp://www.wsdot.wa.gov/Publications/Manuals/M55-05.htmhttp://www.wsdot.wa.gov/Publications/Manuals/M41-10.htmhttp://www.wsdot.wa.gov/Publications/Manuals/M41-10.htmhttp://www.wsdot.wa.gov/Publications/Manuals/M41-10.htmhttp://www.wsdot.wa.gov/Publications/Manuals/M41-10.htmhttp://1360.pdf/http://1140.pdf/http://1130.pdf/http://www.wsdot.wa.gov/Publications/Manuals/M41-10.htmhttp://www.wsdot.wa.gov/Publications/Manuals/M41-10.htmhttp://www.wsdot.wa.gov/Publications/Manuals/M55-05.htmhttp://www.wsdot.wa.gov/Publications/Manuals/M55-05.htm


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Page 1250-2 WSDOT Design Manual M 22-01.05June 2009

Superelevation Chapter 1250

superelevation (super) The rotation of the roadway cross section in such a manneras to overcome part of the centrifugal force that acts on a vehicle traversing a curve.

superelevation runoff The length of highway needed to accomplish the changein cross slope from a section with adverse crown removed (level) to a fullysuperelevated section, or vice versa.

superelevation transition length The length of highway needed to change the crossslope from normal crown or normal pavement slope to full superelevation.

tangent runout The length of highway needed to change the cross slope fromnormal crown to a section with adverse crown removed (level).

traveled way The portion of the roadway intended for the movement of vehicles,exclusive of shoulders and lanes for parking, turning, and storage for turning.

turning roadway A curve on an open highway, a ramp, or the connecting portion ofroadway between two intersecting legs of an intersection.

1250.04 Superelevation Rate Selection

The maximum superelevation rate allowed is 10%.Depending on design speed, construct large-radius curves with a n ormal crownsection. The minimum radii for normal crown sections are shown i n Exhibit 1250- 1 .Superelevate curves with smaller radii as follows:

Exhibit 1250-4a (emax =10%) is desirable for all open highways, ramps, andlong-term detours, especially when associated with a main line detour.

Exhibit 1250-4b (emax=8%) may be used for freeways in urban design areasand areas where the emax=6% rate is allowed but emax =8% is preferred.

Exhibit 1250-4c (emax =6%) may be used, with justi cation, for nonfreewaysin urban design areas, in mountainous areas, and for short-term detours, whichare generally implemente d and removed in one construction season.

Exhibit 1250-5 may be u sed for turning roadways at intersections, for urbanmanaged access highways with a design speed of 40 mph or less, andwith

justi cationfor ramps in urban areas with a design speed of 40 mph or less.

When selecting superelevation for a curve, consider the existing curves on thecorridor. To maintain ro ute cont inuity and driver expectance on open highways, selectthe chart (see Exhibits 1250-4 a, 4 b , or 4c) that best matches the superelevation on theexisting curves.

In locations that experience regular accumulations of snow and ice, limitsuperelevation from the selected chart to 6% or less. In these areas, provide

justi cation for superelevation rates greater than 6%. Vehicles moving at slow speeds

or stopped on curves with supers greater than 6% tend to slide inward on the radius(downslope).

Round the selected superelevation rate to the nearest full percent.


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Design Speed (mph) Minimum Radius for NormalCrown Section (ft)

15 945

20 1,680

25 2,430

30 3,325

35 4,360

40 5,545

45 6,860

50 8,315

55 9,920

60 11,675

65 13,130

70 14,675

75 16,32580 18,065

Minimum Radius for Normal Crown SectionExhibit 1250-1

1250.05 Existing CurvesEvaluate the supe relevation on an existin g curve to determine its adequacy.Use the equation in Exhibit 1250-2 to det ermine the minimum radius for a givensuperelevation and design speed.

f eV R

26.68

Where: R = The minimum allowable radius of the curve (ft)V = Design speed (mph)e = Superelevation rate (%)

f = Side friction factor from Exhibit 1250-3

Minimum Radius for Existing CurvesExhibit 1250-2

For Preservation projects where the existing pavement is to remain in place, the

superelevation on existing curves may be evaluated with a ball banking analysis.Address superelevation when the existing radius is less than the minimum radiuscalculated using the equation or when the maximum speed determined by a ball

banking analysis is less than the design speed. Wh en modifying the sup erelevationof an existing curve, provide superelevation as giv en in 1250.04 .


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Design Speed (mph) Side Friction Factor (f)

15 32

20 27

25 23

30 2035 18

40 16

45 15

50 14

55 13

60 12

65 11

70 10

75 9

80 8

Side Friction Factor Exhibit 1250-3

1250.06 Turning Movements at IntersectionsCurves associated with the turning movements at intersections are superelevatedusing the rates for low-speed urban roadway curves. Use supereleva tion rates as hig has practicable, consistent with curve length and climatic conditions. Exhibit 1250-5 shows the minimum superelevation for the given design speed and radius. Whenusing high superelevation rates on short curves, provide smooth transitions with

merging ramps or roadways.

1250.07 Runoff for Highway CurvesProvide tran sitions for all superelevated highway curves as speci ed in Exhibits1250-6a thr oug h 6e. Which transition to use depends on the location of the pivot

point, the direction of the curve, and the roadway cross slope. The length of therunoff is based on a maximum allowable difference between the grade at the pivot

point and the grade at the outer edge of traveled way for one 12-foot lane.

Pay close attention to the pro le of the edge of traveled way created by thesuperelevation runoff; do not let it appear distorted. The combination ofsuperelevation transition and grade may result in a hump and/or dip in the pro le of

the edge of traveled way. When this happens, the transition may be lengthened toeliminate the hump and/or dip. If the hump and/or dip cannot be eliminated this way,

pay special attention to drainage in the low areas to prevent ponding. Locate the pivot point at the centerline of the roadway to help minimize humps and dips at the edge ofthe traveled lane and reduce the superelevation runoff length.


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When reverse curves are necessary, provide suf cient tangent length for completesuperelevation runoff for both curves (that is, from full superelevation of the rstcurve to level to full superelevation of the second curve). If tangent length islonger than this but not suf cient to provide full super transitions (that is, from fullsuperelevation of the rst curve to normal crown to full superelevation of the secondcurve), increase the superelevation runoff lengths until they abut. This provides onecontinuous tr ansition, wi thout a n ormal crown section, similar to Designs C 2 andD2 in Exhibi ts 1250-6c and 6d, except that full super will be attained rather than thenormal pave ment slope a s shown.

Superelevation runoff on structures is permissible but not desirable. Whenever practicable, strive for full super or normal crown slopes on structures.

1250.08 Runoff for Ramp CurvesSuperelevation runoff for ramps use the same maximum relative slopes as the speci cdesign speeds used for highway curves. Mult ilane ramps h ave a width similar tothe width for highway lanes; therefore, Exhib its 1250-6a throug h 6e ar e used todetermine the superelevation runoff for ramps. Single-lane ramps have a lane widthof 15 feet in curves, requiring the runoff length to be adjusted. S uperelevati on transition lengths (L T) for single-lane ramps are given in Exhibi ts 1250-7a and 7b.Additional runoff length for turning roadway widening is not required.

1250.09 DocumentationFor the list of documents required to be preserved in the Design DocumentationPackage and the Project File, see the De sign Documentation Checklist:

www.wsdot.wa.gov/design/projectdev/
http://www.wsdot.wa.gov/design/projectdev/http://www.wsdot.wa.gov/design/projectdev/http://www.wsdot.wa.gov/design/projectdev/http://www.wsdot.wa.gov/design/projectdev/http://www.wsdot.wa.gov/design/projectdev/


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S u p e r e

l e v a t i o n

( % )

5 5 m p h

7 0 m p h 6 0 m p h

5 0 m p h

6 5 m p h

7 5 m p h

Design Speed (mph) 15 20 25 30 35 40 45 50 55 60 65 70 75 80

Minimum Radius (ft) 40 75 130 205 295 415 545 700 880 1095 1345 1640 1980 2380

Superelevation Rates (10% Max)Exhibit 1250-4a


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2 5 m p h

S u p e r e

l e v a t i o

n ( % )

5 0 m p h

Design Speed (mph) 15 20 25 30 35 40 45 50 55 60 65 70 75 80


Superelevation Rates (8% Max)Exhibit 1250-4b


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Design Speed (mph) 15 20 25 30 35 40 45 50 55 60 65 70 75 80


Superelevation Rates (6% Max)Exhibit 1250-4c


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e (%)

LB=Basic Runoff in Feet for Design Speed*

15mph

20mph

25mph

30mph

35mph

40mph

45mph

50mph

55mph

60mph

65mph

70mph

75mph

80mph

2 30 30 35 35 40 40 45 50 50 55 55 60 65 70

3 45 50 50 55 60 60 65 70 75 80 85 90 95 105

4 60 65 70 75 75 85 90 95 100 105 110 120 125 135

5 75 80 85 90 95 105 110 120 130 135 140 150 160 170

6 90 95 105 110 115 125 135 145 155 160 170 180 190 205

7 110 115 120 130 135 145 155 170 180 185 195 210 220 240

8 125 130 135 145 155 165 180 190 205 215 225 240 250 275

9 140 145 155 165 175 185 200 215 230 240 250 270 285 310

10 155 160 170 180 195 205 220 240 255 265 280 300 315 345

* Based on one 12-ft lane between the pivot point and the edge of traveled way. When the distance exceeds 12 ft,use the following equation to obtain L R:

LR=LB(1+0.04167X)Where:X = The distance in excess of 12 ft between the pivot point and the farthest edge of traveled way, in ft.

e

ec

RL

e

c

RL

e

c

RL

1 0 0

w c n

100

wcn

1 0 0

w e n

Design A Pivot Point on Centerline Crown Sectionc = Normal crown (%)e = Superelevation rate (%)n = Number of lanes between pointsw = Width of lane

Superelevation Transitions for Highway CurvesExhibit 1250-6a


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e

c

RL

1 0 0

w c n

1 0 0

w e n

B e g

i n ( e n

d )

f u l l s u p e r

P C

o r

P T

B e g

i n ( e n

d )

t r a n s

i t i o n

Design C1

Pivot Point on Centerline Curve in Direction of Normal Pavement Slope: Plane Section

e

c

RL

e

ec

RL

B 1 0 0

w c n

LR

e

c

RL

1 0 0

w e n

E d g e o f t r a v e l e d w a y i n s i d e o f c u r v e

B e g

i n ( e n

d )

f u l l s u p e r

P C

o r

P T

0.7L R 0.3L R

CLPivot point

B e g

i n ( e n

d ) t r a n s

i t i o n

BC

A

A

E d g e o f t r a v e l e d w

a y

o u t s i d e o f c u r v e

A BPivot point

C

C r o w n s l o p e C r o w n s l o p e

C

F u l l s u p e r

Design C2 Pivot Point on Centerline Curve

Opposite to Normal Pavement Slope: Plane Section

c = Normal crown (%)e = Superelevation rate (%)n = Number of lanes between pointsw = Width of lane

Superelevation Transitions for Highway CurvesExhibit 1250-6c


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1 0 0

w c n

e

c

RL

Edge of traveled way outsideof curve pivot point

B

LR

1 0 0

w e n

E d g e o f t r a v e l e d w a y i n s i d e o f c u r v e

B e g

i n ( e n

d )

f u

l l s u p e r

P C

o r

P T

0.7L R 0.3L R

B e g

i n ( e n

d )

t r a n s

i t i o n

B

C r o w n s l o p e

A B

C r o w n s l o p e

Pivot pointF u l l s u p e r

A A

Design D 1 Pivot Point on Edge of Traveled Way Curve in Direction of Normal Pavement Slope: Plane Section

e

c

RL

e

ec

RL

Edge of traveled way insideof curve pivot point

A 1 0 0

w c n

LR

e

c

RL

1 0 0

w e n

B e g

i n ( e n

d )

f u l l s u p e r

P C

o r

P T

0.7L R 0.3L R

B e g

i n ( e n

d ) t r a n s

i t i o n

AB

E d g e o f t r a v e l e d w

a y

o u t s i d e o f c u r v e

A B

C r o w n s l o p e

Pivot point

C r o w n s l o p e

B

F u l l s u p e r

Design D2 Pivot Point on Edge of Traveled Way Curve

Opposite to Normal Pavement Slope: Plane Sectionc = Normal crown (%)e = Superelevation rate (%)n = Number of lanes between points

w = Width of lane

Superelevation Transitions for Highway CurvesExhibit 1250-6d


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F u l l S u p e r

LT.

100W L e

B e g

i n ( e n

d )

f u l l s u p e r

P C

o r

P T

CLPivot point

B e g

i n ( e n

d )

t r a n s

i t i o n

Pivot point

C r o w n S l o p e

0.02 W L

2

20.3L0.7L TT

e

2

2LL0.3 TT

e

e(%)

Length of Transition in Feet for Design Speed20 mph 25 mph 30 mph 35 mph 40 mph 45 mph 50 mph 55 mph

LT LT LT LT LT LT LT LT3 10 15 15 15 15 15 15 154 20 25 25 25 25 30 30 355 30 35 35 35 40 45 45 506 40 45 45 50 55 55 60 657 50 55 55 60 65 70 75 808 60 65 70 75 80 85 90 959 70 75 80 85 95 100 105 110

10 80 85 90 100 105 115 120 130Table 1 Pivot Point on Centerline: Curve in Direction of Normal Pavement Slope

LT.

100

W L e

B e g

i n ( e n

d )

f u l l s u p e r

CLPivot point

B e g

i n ( e n

d )

t r a n s

i t i o n

Pivot point

C r o w n S l o p e

0.02 W L

2

2LL0.3 TT

e

F u l l S u p e r

P C o r

P T

2

2LL0.7 TT

e

2

2L T

e

Level

e(%)


LT LT LT LT LT LT LT LT2 40 40 45 50 55 55 60 653 50 55 55 60 65 70 75 804 60 65 70 75 80 85 90 955 70 75 80 85 90 100 105 1106 80 85 90 95 105 115 120 1307 90 95 100 110 120 125 135 1458 100 105 115 120 130 140 150 1609 110 120 125 135 145 155 165 175

10 120 130 135 145 160 170 180 190Table 2 Pivot Point on Centerline: Curve in Direction Opposite to Normal Pavement Slope

WL = Width of ramp laneSuperelevation Transitions for Ramp Curves

Exhibit 1250-7a


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F u l l S u p e r

LT.

100W L e

B e g

i n ( e n

d )

f u l l s u p e r

P C

o r

P T

CLPivot point

B e g

i n ( e n

d )

t r a n s

i t i o n

C r o w n S l o p e

Pivot point

0.02 W L

2

20.3L0.7L TT

e

2

2LL0.3 TT

e

e(%)


LT LT LT LT LT LT LT LT3 20 25 25 25 25 30 30 354 40 45 45 50 55 55 60 655 60 65 70 75 80 85 90 956 80 85 90 100 105 115 120 130

7 100 105 115 120 130 140 150 1608 120 130 135 145 160 170 180 1909 140 150 160 170 185 195 210 225

10 160 170 180 195 210 225 240 255Table 3 Pivot Point on Edge of Traveled Way: Curve in Direction of Normal Pavement Slope

LT.

100

W L e

B e g

i n ( e n

d )

f u l l s u p e r

CLPivot point

B e g

i n ( e n

d )

t r a n s

i t i o n

Pivot point

C r o w n S l o p e

0.02 W L

2

2LL0.3 TT

e

F u l l S u p e r

P C

o r

P T

2

2LL0.7 TT

e

2

2L T

e

Level

e (%)


LT LT LT LT LT LT LT LT2 80 85 90 100 105 115 120 1303 100 105 115 120 130 140 150 1604 120 130 135 145 160 170 180 1905 140 150 160 170 185 195 210 2256 160 170 180 195 210 225 240 2557 180 190 205 220 235 255 270 2908 200 210 225 245 265 280 300 3209 220 235 250 265 290 310 330 350

10 240 255 270 290 315 340 360 385Table 4 Pivot Point on Edge of Traveled Way: Curve in Direction Opposite to Normal Pavement Slope

WL = Width of ramp lane

Superelevation Transitions for Ramp CurvesExhibit 1250-7b

Superelevation Guidlines

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