Highway Geometric Standard

8/13/2019 Highway Geometric Standard

1/38

1

By

Rini Srivastava

B.Tech ,IV Yr.(Civil Engg)

BBDESGI


2/38


3/38

Basic Principles of Geometric Design Cross-Sectional Elements

Pavement surface characteristics

- Road Land Width- Road way Width

- Carriageway Width

- Shoulder Width- Side Slopes

Sight Distances SSD, ISD, OSD

Horizontal and vertical alignment details 3


4/38

Topography-Tarrain classification

Design speed

Traffic factors-Design vehicle

Design hourly volume and capacity Environment and other factors.

4


5/38

5

TERRAIN CLASSIFICATION

Terrain

Classification

Percent cross-slope of the

country

Plain 0-10

Rolling 10-25

Mountainous 25-60

Steep >60


6/38

6

Classification

Plaintarrain

Rollingtarrai

n

MountaniousTarrai

n

SteepTarrain

Ruling Min. Ruling Min. Ruling Min. Ruling Min.

NH andSH 100 80 80 65 50 40 40 30

MDR 80 65 65 50 40 30 30 20

ODR 65 50 50 40 30 25 25 20

Village 50 40 40 35 25 20 25 20

Expressway 120 K.P.H


7/38


8/38

8


9/389

Terrain Roadway Width (metres)

Plain and Rolling 7.5

Mountainous and

Steep6.0

1. Above widths are exclusive of parapets and side drains.

2. In hilly and mountainous terrains, lay byes 3.75m wideand 20m long should be provided atleast at the rate of two

per kilometre. These should be judiciously located

considering the aspect of visibility.


10/38

At Culvert : Plain & Rolling 7.5m

Mountainous 6.0m

At Bridge : Clear roadway 5.5 (exclusiveparapet)

At Cause way : Plain & Rolling 7.5mMountainous 6.0m

10


11/3811


12/3812


13/38


14/38

14

V Kmph 20 - 30 40 50 60

f 0.4 0.38 0.37 0.36


15/38

15

Overtaking Sight Distance (OSD)

OSD = 0.28Vb

t + 0.28Vb

T + 2s + 0.28 VT...m

Vb = Speed of Overtaken Vehicle

V = Design Speed

t = reaction time (2 to 2.5 seconds)

s = spacing of vehicles = (0.2 Vb +6) ...m

T = 14.4 s/A

A = Acceleration Kmph/sec.

V, Kmph 25 30 40 50 65

A, Kmph/sec 5.00 4.80 4.45 4.00 3.28


16/38

ISD = 2 x SSD ...m

16


17/38

17

Speed(Km/hr.)

Safe StoppingSight Distance

(metres)

IntermediateSight Distance

(metres)

OvertakingSight Distance

(metres)

20 20 40 -

25 25 50 -

30 30 60 -

40 45 90 165

50 60 120 235


18/38


19/38

19

Horizontal Alignment Vertical Alignment

General

Horizontal curvesSuper elevation

Minimum curve radii

Transition curve

Widening of curvesSet back distances

Gradients

Grade compensationSummit curve

Valley curve


20/38

20

Design of Horizontal Curve:

Absolute minimum values based on minimum design speed may

be used where economy of construction and site conditions so dictates.

The radii below the absolute minimum should not be provided

Straight sections exceeding 3 km length should be avoided. A

curve liner alignment with long curve is better from point of safety and

aesthetic.

Curve should be sufficiently long and have suitable transition

curves at both the ends.

Reverse curves may be needed in difficult terrains.


21/38

21

Design of Horizontal Curve:Contd.

Design Factors:

1. Design Speed (Kmph)

2. Super elevation

3. Spiral Transition Curves at both the ends

4. Coefficient of (side) friction (f)


22/38

22


23/38

23

e + f = V2 / g.R e = rate of super elevation

R = Radius of Curve (m)

e = V2/ 225 R

Limitations of Super elevation

Plain & Rolling Terrain =Maximum 7%

Snow bound area =Maximum 7%

Hilly Area but not snow bound =Maximum 10%


24/38

Length of transitioncurveis determined onthe basis of rate ofchange of centrifugalacceleration or rate ofchange of superelevation.

Spiral Curve

should be used forTransition Curve.

24

1. Transition Curve

improves aesthetic

appearance.

2. Super elevation & extra

widening are gradually

introduced.


25/38

Based on rate of change of centrifugal acceleration.

Ls = 0.0215 V3

/ C.R ....mC = rate of change of centrifugal acceleration

C = 80/(75+V).. m/ sec3(Limiting 0.5 C 0.8)

Based on rate of introduction of super elevation.Ls= (e x N) x (W+We) /2...m(When the Pavement is rotated about central line)1 in N is the rate of introduction of super elevation

N = 150 (for plain terrain)N = 60 (for hilly terrain)

25


26/38

By empirical method.

Ls = 2.7 V2 / R...m (for plain & rolling

terrain)

Ls= V2/ R...m (for mountainous terrain)

26


27/38


28/38

Set back distance (m) = R R Cos /2 ...m

/2 = 180 x S/ (2R)

S = Stopping sight distance in m

Set back distances for different speeds

28

V Kmph 20 25 30 40 50

Set back (m)

m

20 25 30 45 60


29/38

29

Mountainous Steep

Snow-bound Not snow-

bound

Snow-bound Not snow-

bound

Ruling

minim

um

Absol

ute

minim

um

Ruling

minim

um

Absol

ute

minim

um

Ruling

minim

um

Absolu

te

minim

um

Ruling

minimu

m

Abso

lute

mini

mum

23 15 20 14 23 15 20 14


30/38

30

Plain Terrain Rolling Terrain

Ruling

minimum

Absolute

minimum

Ruling

minimum

Absolute

minimum

90 60 60 45

Ruling minimum and absolute minimum radii are for

ruling design speed and minimum design speed

respectively.


31/38


32/38

32

Terrain Type Ruling Gradient%

LimitingGradient %

ExceptionalGradient %

Plain or Rolling

Mountainous

Steep

(a) Up to 3000m

in heightabove MSL

(b) Height more

than 3000m

above MSL

3.3

5

6

5

5

6

7

6

6.7

7

8

7


33/38

33

Condition Slope

(horizontal : vertical)

Embankment in silty/sandy/gravelly soil 2:1

Embankment in clay soils or

inundated conditions 2.5 :1 to 3:1

Cutting in silty/sandy/gravelly soil 1:1 to 0.5 :1

Cutting in disintegrated rock or conglomerate 0.5 :1 to1/8 :1

Cutting in medium rock (e.g sandstone)1/12 :1 to1/16 :1

Cutting in hard rock Near Vertical

On high embankments like bank of a canal or flood production

bund, side slopes should be designed as per IRC Guidelines for the

design of high embankments.


34/38

34

At horizontal curves, gradient should be eased by a certainamount as calculated by the following formula:

Grade Compensation = (30+R) /R

subject to a maximum of where R is the radius of curve in

metres.

Grade Compensation should be so applied that it does not

make the grades flatter than 4%.


35/38

35

Vertical curves should be provided at all grade changes exceeding 1 percent.

Vertical curves are of two types viz. Summit curves and Valley curves

The length of summit and valley curves can be calculated as under:

Summit Curves

When L>S, L = NS/4.4,

When LS, L = NS / (1.5+0.035 S)

When L


36/38

36


37/38

37

IRC:86-1983 Geametric Design Standards for urban roads

in plains

Highway Engineering by Khanna and Justo


38/38

Documents

Highway Geometric Standard