Geometric design of highways Mr. Desai Akshay Prakash Lecturer in civil engineering department Sant Gajanan Maharaj Rural Polytechnic, Mahagaon. contact-+91-9604713468 www.sgmrh.com

1. Mr. Desai A. P.
SGMRP, Mahagaon.
Mr. Desai A. P.

2. Geometric Design Of Highways
 The Phase Of Highway Design Which Deals
With The Visible Elements Of Highways Such As
Alignment, Sight Distance, Curve, Super
elevation Etc. Is Called as Geometrical Design Of
Highways.
 Speed, Safety And Comfort Should Be The
Main Characteristics Of The Road Way This
Depend On The Proper Geometric Design.
 The Geometric Design Should Be According
To Nature Of Terrain For Economy.
Mr. Desai A. P.

3. Classification Of Terrain
% slope of the
country
classification
0-10 Plain
10-25 Rolling
25-60 Mountainous
More than 60% steep
Mr. Desai A. P.

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6. Right of way
The area of the land acquired for construction and
development of a road along its alignment is known as
right of way.
the width of this acquired land is known as
‘land width’
Road
classification
Plain and rolling
terrain
Mountainous and
steep terrain
National highway,
State highways
45 24
M.D.R. 25 18
O.D.R. 15 15
V.R. 12 09Mr. Desai A. P.

7. Road way width
The road way width is the total width of
carriage way with shoulders on both sides.
Road
classification
Plain and rolling
terrain (M)
Mountainous
and steep (M)
NH & SH
1) Single lane
2) Two lane
12
12
6.25
8.80
M.D.R.
1) Single lane
2) Two lane
09
09
4.75
-
O.D.R.
1) Single lane
2) Two lane
7.5
09
4.75
-
V.R. 7.5 4
Mr. Desai A. P.

8. Road Margin
This is the portion of land width on either
side of roadway of a road. This margins are used
for parking lanes, frontage roads, driving way,
footpath, side drain and side slopes.
Carriage way-
The portion of roadway constructed for
movement of vehicular traffic is called carriage
way.
Mr. Desai A. P.

9. On V.R. carriage way width may be limited to 3 m
No. of lanes Width of carriage
way (M)
Single lane 3.75
Two lane without raised
kerb
7.00
Two lane with raised kerb 7.5
Intermediate carriage way 5.5
Multi lane pavement 3.5
Mr. Desai A. P.

10. Shoulder
Shoulder are strips provided on either side of
carriage way having enough strength to support to
the loaded vehicles.
Shoulders are also used for cycle track,
pedestrian track etc.
Shoulders provide space for breakdown
vehicles.
Shoulders are given outward slope to drain
off water quickly.
Shoulder width recommended by IRC is 2.5 M.
Mr. Desai A. P.

11. Side slopes
Slopes given to side of earthwork of road in
embankment or in cutting for its stability is called
side slopes. Generally 2:1 slope is given in filling
and 1:1 slope is given in cutting.
Berms
Berms prevent side slopes of road
embankment from damage by lateral thrust due
spoil bank. Also it gives lateral stability to the slope
of road embankment.
Mr. Desai A. P.

12. Spoil bank
The banks constructed from surplus
excavated earth on the side of road cutting
parallel to its alignment are known as spoil bank.
Kerb
The boundaries between the pavement and
shoulder or footpath are known as kerbs.
Mr. Desai A. P.

13. Formation level
R.L. of finished surface of earthwork of road
in embankment or in cutting is called formation
level. The formation level for the road in
embankment should be kept above HFL (high
flood level)
The formation level for the road in cutting
should be sufficiently above ground water table.
Mr. Desai A. P.

14. Camber
Camber or cross slope is the slope provided
to the road surface in transverse direction to drain
off rain water from road surface.
camber is defined as slope of the line joining
the crown and edge of the road surface.
camber is expressed in 1 in n i. e. 1 vertical
to n horizontal. Camber is also expressed in %
Amount of camber depends upon,
1. Intensity of rainfall
2. Permeability of road surfacing material
Mr. Desai A. P.

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17. Purpose of providing camber
1. To prevent the entry of surface water or rain
water into the sub grade soil through
pavement. If water enters into the subgrade,
stability and life of pavement gets adversely
affected.
2. To allow pavement get dry soon after the rain,
so that it should not become sleepary and
unsafe for vehicles.
Mr. Desai A. P.

18. IRC Recommendations
Sr.
no.
Type of surface camber
1 Cement concrete road and
high type bituminous type
road
1 in 60 to 1 in 50
(1.7 to 2 %)
2 Thin bituminous surface 1 in 50 to 1 in 40
(2.5 to 2 %)
3 W.B.M. 1 in 40 to 1 in 33
(2.5 to 3%)
4 Earthen road 1 in 33 to 1 in 25
(3 to 4%)
Mr. Desai A. P.

19. TYPES OF CAMBER
1. Composite camber-The camber which consist
of two straight slopes from edges with a circular or
parabolic curve in the center of carriage way.
2. Straight camber- when two straight slopes from
the edges joints at a center of carriage way, then
such camber is known as straight camber.
3. Two straight line camber- when camber consist
of two straight line steeper near the edges and
flater near the crown of carriage way, then such
camber is known as two straight line camber.
Mr. Desai A. P.

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22. Barrel camber-
This camber consist of a continuous
curve that may be either parabolic or
elliptical
Mr. Desai A. P.

23. Gradient
Gradient is the rate of rise or fall
along the length of the road with
respect to horizontal.
It is expressed as 1 in n or %
Gradient = 𝑣𝑒𝑟𝑡𝑖𝑐𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
ℎ𝑜𝑟𝑖𝑧𝑜𝑛𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
x100
=ℎ
𝐷
x100
Mr. Desai A. P.

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26. Object or purpose of gradient
1.To connect the stations located at
different levels.
2. To make the earthwork of the road
project economical by balancing cutting
and filling.
3. To provide effective drainage of rain
water.
4. To construct side drain economically.
Mr. Desai A. P.

27. Factors affecting gradient
1.Nature of ground
2. Nature of traffic
3.Drainage required
4.Type of road surface
5.Total height to be covered
Mr. Desai A. P.

28. Types of gradient
1. Ruling gradient- it is the gradient within which
the vertical profile of the road is design, hence
it is called as design gradient. This is such a
gradient that all vehicle can use road without
extra consumption of fuel or much cutting.
2. limiting gradient- where topography of the
place compels to adopt steeper gradient than
ruling gradient, limiting gradient is used
because the road with flatter gradient will be
very costly. However the limiting gradient is
used in restricted road length.Mr. Desai A. P.

29. 3. Exceptional gradient- the gradient steeper than
the limiting gradient is known as exceptional
gradient and it is used in extra ordinary situation
for shorter lengths of the road.
4. Average gradient- the total rise or fall between
any two points along the alignment of a road
divided by the horizontal distance between them
is called average gradient
Mr. Desai A. P.

30. 5.Floating gradient- the gradient on which a
motor vehicle moving with a constant speed
contineous to descend with same speed without
any application of power or break is called
floating gradient.
6. Minimum gradient- the minimum desirable
slope essential for effective drainage of rain water
from the road surface is called as minimum
gradient.
Mr. Desai A. P.

31. IRC Recommendations
Sr.no. Nature of the area Gradient
Rulling Limiting Exceptional
01 Plain or rolling area 1 in 30
(3.3%)
1 in 20
(5%)
1 in 15
(6.7%)
02 Mountainous 1 in 20
(5%)
1 in 16.7
(6%)
1 in 14.7
(7%)
03 Steep area 1 in 16
(6%)
1 in 14.3
(7%)
1 in 12.5
(8%)
Mr. Desai A. P.

32. Sight distance
The distance along the center line of road at
which a driver has visibility of an object,
stationary or moving at a specified height above
the carriage way is known as ‘sight distance’
The longest distance the driver can see in
front of him is called sight distance.
For safe driving, certain minimum sight
distance are considered-
Mr. Desai A. P.

33. Factors affecting sight distance
1. Speed of the vehicle.
2. The frictional resistance of the road
surface.
3. Height of the drivers eye.
4. Slope of the road surface.
5. Perception time and break reaction time.
Mr. Desai A. P.

34. Perception time
Perception time is the time required for a
driver to realized that break must be applied.
It is the time from the instant the object comes
on the line of sight of the driver to the instant he
realized that the vehicle need to be stop.
Break reaction time- it is brief interval between
the perception of the danger and the effective
application of the break.
Mr. Desai A. P.

35. Types of sight distance
Safe stopping or non-passing sight distance-
The clear distance ahead needed by the
driver to stop his vehicle before meeting and
object on his way is known as safe stopping sight
distance or non-passing sight distance.
Mr. Desai A. P.

36. Safe Overtaking Sight Distance
The minimum distance available to the
vision of the driver intending to overtake a slow
moving vehicle ahead with safety against the
traffic of opposite direction is known as OSD.
OSD Depends Upon
1. Speed of overtaking and overtaken vehicles.
2. Spacing between the two vehicles.
3. Feel and reaction time of the driver.
4. Rate of acceleration of overtaking vehicle.
Mr. Desai A. P.

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38. 4. Gradient of the road.
d1= distance travelled by overtaking vehicle ‘A’
from A1 to A2.
d2= distance travelled by overtaking vehicle ‘A’
from A2 to A3 during overtaking operations.
d3= distance travelled by incoming vehicle ‘C’
from C1 to C2 during overtaking operation of ‘A’.
Mr. Desai A. P.

39. A is the overtaking vehicle originally traveling at
design speed ‘V’ Kmph.
B is the overtaken vehicle with speed ‘Vb’ kmph.
C is the vehicle coming from opposite direction
at ‘Vc’ kmph.
Mr. Desai A. P.

40. IRC recommendations
Speed in kmph O.S.D. IN ‘m’
100 640
80 470
65 340
60 300
50 235
40 165
Mr. Desai A. P.

41. Sight Distance At Intersection
The sight distance needed by the driver of a
vehicle to see another vehicle approaching the
intersection reacts and applying the breaks to
bring his vehicle to stop at the intersection
without any collision or accident is called sight
distance at intersection.
The sight distance at intersection should be
sufficient to satisfy the following conditions.
1. To enable vehicle to change its speed.
Mr. Desai A. P.

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43. 2. To enable vehicle to stop.
3. To enable stopped vehicle to cross a main road.
IRC Recommendations
Speed in kmph Min. ISD in ‘m’
100 220
80 180
65 145
50 110Mr. Desai A. P.

44. Super elevation
In order to counteract the effect of
centrifugal force and to reduce the tendency of
vehicle to overturn, the outer edge of the
pavement is raised with respect to the inner edge,
thus providing a transverse slope through out the
transverse length of the horizontal curve.
This transverse inclination to the pavement is
known as super elevation or cant.
Super elevation ‘e’ is expressed as
e+f= 𝑣2
127𝑅
Mr. Desai A. P.

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46. Where, e= rate of super elevation in ‘m’
F=co-efficient of friction between tyre and
pavement(0.15)
V= design speed in ‘kmph’
R= mean radius.
Super elevation should be limited to the following
values.
1) Plain and rolling country = 7.0% (1 in 15)
2) In hilly terrain= 10% (1 in 10)
3) On urban roads= 4% (1 in 25)
Mr. Desai A. P.

47. Super Elevation
Mr. Desai A. P.

48. Objects of providing super elevation
1. To counteract the effect of centrifugal force
acting on moving vehicle.
2. To negotiate a curved path without overturning
and skidding.
3. To ensure smooth and safe movements of
passengers and goods on the road.
4. To prevent damaging effect on the road surface
due to improper distribution of load.
5. The maintenance cost of road on curve is
reduced. Mr. Desai A. P.

49. Super elevation depends on
following factors
1. Coefficient of friction between tyres and
pavements.
2. Speed or design speed in kmph
3. Radius of horizontal curve in meter.
4. Topographic conditions.
Mr. Desai A. P.

50. Design speed
The maximum safe speed of vehicles assumed
for geometrical design of highways is knows as
‘design speed’.
Design speed depends upon the following factors
1. Class and condition of the road surface.
2. Nature, intensity and type of traffic.
3. Type of curve along the road.
4. Sight distance required.
5. Nature of the terrain.
6. Structure of the road.
Mr. Desai A. P.

51. IRC Recommendations
Road
classification
Design speed in kmph
Plain
terrain
Rolling
terrain
Mountainous
terrain
Steep
terrain
Expressway,
NH, SH
100 80 50 40
M.D.R. 80 65 40 30
O.D.R. 65 50 30 25
V.R. 50 40 25 25
Mr. Desai A. P.

52. Widening of road pavement
• On horizontal curves, especially when they are
not of very large radius, it is common to widen
the pavement slightly more than the normal
width.
• The object of providing extra widening of
pavements on horizontal curves are due to the
following reasons.
• 1 an automobile has a rigid wheel base and only
the front wheels can be turned when this vehicle
takes a turn to negotiate a horizontal curve, the
rear wheels do not follow the same path as that of
the front wheel.
Mr. Desai A. P.

53. • This phenomenon is called off tracking.
Normally the rear wheels follow the inner path
on the curve as compared with those of the
corresponding front wheels. This means that if
inner front wheels takes a path on the inner
edge of a pavement at a horizontal curve,
inner rear wheel will be off the pavement on
the inner shoulder. The off tracking depends
upon the length of the wheel base of the
vehicle and the turning angle, or the radius of
the horizontal curve.
Mr. Desai A. P.

54. • 2. At speeds higher than the design speeds
when the super elevation and lateral friction
developed are not fully able to counteract the
outwards thrust due to the centrifugal force,
some transverse skidding may occur and the
rear wheels may take paths on the outside of
those traced by the front wheels on the
horizontal curve. However this occurs only at
excessively high speeds
Mr. Desai A. P.

55. • 3. in order to take curved path with larger
radius and to have greater visibility at curve,
the drivers tendency not to follow the central
path of the lane, but to use the outer side at the
beginning of a curve.
• 4. while two vehicles cross or overtake at
horizontal curve there is a psychological
tendency to maintain a greater clearance
between the vehicles, than on straight for
increase safety.
Mr. Desai A. P.

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58. Mechanical widening (𝑊𝑚)
• The widening required to account for the
off-tracking due to the rigidity of wheel
base is called Mechanical widening.
• 𝑊𝑚= 𝑛𝑙2
2𝑅
Mr. Desai A. P.

59. Psychological Widening (𝑊𝑝𝑠)
• Extra width of pavement is also provided for
psychological reason such as, to provide for
greater maneuverability of steering at higher
speeds, to allow for the extra space
requirements for the overhangs of vehicles and
to provide greater clearance for crossing and
overtaking vehicles on the curve.
• 𝑊𝑝𝑠= 𝑉
9.5 𝑅
Mr. Desai A. P.

60. Total Widening (𝑊𝑒)
𝑊𝑒 = 𝑛𝑙2
2𝑅
+ 𝑉
9.5 𝑅
Hence n= number of traffic lanes
l= length of wheel base of longest vehicle, m.
The value of l may normally be taken as 6.1 m or
6.0 m for commercial vehicles.
V = Design speed, Kmph
R = Radius of Horizontal Curve, M
Mr. Desai A. P.