The document discusses various types of road intersections, their classifications, and design elements, including at-grade and grade-separated intersections, traffic islands, T and Y intersections, rotary intersections, and terminal facilities. It outlines the requirements for intersection design to enhance safety, visibility, and traffic flow, while also addressing the advantages and disadvantages of channelized intersections and traffic islands. The document provides specific data on design speeds, safe stopping distances, and the impact of different intersection shapes on vehicular movement and safety.

1. PREPARED BY:- KHUSHBU TEKWANI

2. CONTENTS
 Introduction
 Intersections
 Traffic Islands
 Conflicts at Intersection
 Visibility at Intersection
 Widths of carriageway at Intersection
 Median Openings
 T- Intersection
 Y- Intersection
 Cross roads and Staggered Intersection
Rotary Intersection
 Rotary design elements
Grade Separated Intersections
Terminal Facilities

3. INTRODUCTION
 Basic geometric elements are:-
Intersections at Grade
Grade Separated
intersections (interchange)
Traffic Islands
Terminal Facilities

4. INTERSECTIONS
 Intersection is the location on a roadway where two or
more approaches from different directions are
meeting.

5. INTERSECTION
 Road intersections can be divided in two groups:-
A. Intersection at Grade
B. Grade separated Intersection

6. A) INTERSECTION AT GRADE
 All roads meet at more or less the same level involved in
the intersection at grade.
INTERSECTION AT GRADE
Unchannelized
Intersection
Channelized
Intersection
Rotary
Intersection

7. Classification of Intersection at Grade
A) According to Shape:-
 Three legged intersection (T, Y and skewed)
 Four legged intersection (Right angled, skewed, offset)
 Rotary intersection
B) According to Geometric design features:-
 Unchannalized intersection
 Channelized intersection
C) According to traffic control:-
 Uncontrolled intersection
 Controlled Intersection
 Signalized intersection
D) According to levels of crossing:-
 At grade intersections
 Grade separated intersections

9. FORMS OF INTERSECTION

10. Requirements of intersection at Grade
At the intersection the area of conflict should be as
small as possible.
For the vehicles, adequate visibility should be
available.
The relative speed and angle of approach of
vehicles should be small.
Sudden change of path should be avoided.
Proper signs should be provided.
Proper lighting should be provided for better
visibility at night.

11. Unchannelized Intersections
 The intersection area is paved and there is absolutely
no restriction to vehicle to use any part of intersection
area.
 Lowest class of intersection
 Easy to design but most complex in traffic operations
resulting in maximum conflict area and more no of
accidents.

13. Channelized Intersections
 Channelized Intersections is achieved by introducing
islands into the intersectional area, thus reducing total
conflict area available.
 These are help to channelize turning traffic, to control
their speed and to decrease conflict area.

15. Advantages of Channelized
Intersections
By channelization, vehicles confined to definite path.
Conflict areas can be decreased.
Angle of merging streams can be forced to be flat
angles so as to cause minimum disruption.
Speed of vehicle can be controlled.
Refuse islands can be provided for pedestrians.
Points of conflicts can be separated.
Signs & traffic devices can be installed.

16. TRAFFIC ISLANDS
 Traffic islands are raised areas constructed within the
roadway to establish physical channels through which
the vehicular traffic may be guided.

17. FUNCTIONS OF TRAFFIC ISLANDS
Functions of Traffic Islands:-
To segregate the pedestrians and vehicles.
To separate traffic into specified paths.
To reduce conflict areas.
To increase safety
To divert traffic from obstacles.

18. ADVANTAGES OF TRAFFIC
ISLANDS
It provides smooth and controlled traffic flow.
It reduces the accident and increase safety
It gives uniform speed of traffic.
No need of police control.

19. DISADVANTAGES OF TRAFFIC
ISLANDS
 It consumes useful traffic area.
 It increases travel distance.
 Width of traffic lane decreases.

20. TYPES OF TRAFFIC ISLANDS
1. Divisional islands
2. Channelizing islands
3. Pedestrian loading islands
4. Rotary islands

21. DIVISIONAL ISLANDS
 These are intended to separate opposing traffic flow
on a highway with four or more lanes.
 Head-on-collision are eliminated.
 Kerbs should be high enough to prevent vehicles from
entering into the islands.

22. CHANNELIZED ISLANDS
 These are used to guide traffic into proper channel
through the intersection area.
 Very useful as traffic control devices for intersection
at grade.

24. PEDESTRIAN LOADING ISLANDS
 They are provided at regular bus stops and similar
places for protection of passengers.
 A pedestrian island near cross walk may be termed as
‘pedestrian refuse islands’.

25. ROTARY ISLANDS
 It is a large central island of a rotary intersection.

26. Conflicts at an Intersection
 Crossing conflicts
 Merging conflicts
 Diverging conflicts

28. VISIBILITY AT INTERSECTIONS
 At intersection where the intersecting roads are of
more or less equal importance & there is no
established priority, visibility should be provided .
 SSD is given by,
 SSD = lag distance + breaking distance

29. SSD values for different speeds
DESIGN SPEED (km.ph) SAFE SSD (m)
20 20
25 25
30 30
40 45
50 60
60 80
65 90
80 120
100 180

30.  It is customary to control traffic on the minor road by
STOP or GIVEWAY sign or road markings.
 Such intersection are known as Priority Intersection.
 Priority to the right is a right-of-way system, in which the
driver of a vehicle is required to give way to vehicles
approaching from the right at intersections.

31. WIDTH OF CARRIAGEWAY
 Width needs to be increased in curves, keeping in mind
mechanical widening and psychological widening.
 Extra Widening = Mechanical Widening +
Psychological Widening
 We = nl ²/2R + V/9.5(R)½

32. MEDIAN OPENINGS
 At Intersections, where nearly all the traffic travels on the
divided highway and volume is below capacity, the
occasional vehicles may use the median opening either to
come to the through road from the cross road or reverse.
 A bullet nosed median opening designed for the minimum
turning path will meet the requirements.
 A bullet nosed median end is preferable.
 The length of opening depends on the width of median.

33. Median opening with bullet nosed end

34. T-INTERSECTION
 It is normally provided for very light traffic and for minor
and local roads.
 For locations where speeds are high and turning
movements are large, it is hazardous.

35. T-INTERSECTION

36. Y-INTERSECTION
 Mostly design features are similar to that of T-
Intersections, except where the intersection angle is very
acute.

37. Y-INTERSECTION

38. CROSS ROADS
 In case of cross roads, two roads crosses approximately at
right angles.
 Uncontrolled cross roads are very dangerous due to high
accident rate.

39. CROSS ROADS

40. STAGGERED INTERSECTION
 The safety at the cross roads can be significantly enhanced
by converting it into a staggered intersection.
 A minimum distance of 35 m is necessary between the
staggered roads.
 A right/left staggered is preferred to left/right stagger
where there are no separate right turning lanes.

41. STAGGERED INTERSECTION

42. STAGGERED INTERSECTION

43. ROTARY INTERSECTION
 A ROTARY INTERSECTION is an enlarged road
intersection where all converging vehicles are forced to
move round a large central island in one direction before
they can weave out of traffic flow into their respective
directions radiating from the central island.
 The main object of providing a rotary are to eliminate the
necessity of stopping even for crossing streams of vehicles
and to reduce area of conflict.

46. ROTARY DESIGN ELEMENTS
Design Speed
Shape of central island
Radius of entry
Radius at exit
Radius of central island
Weaving length
Width of carriage way at entry and exit
Width of rotary carriageway
Entry and exit angles
Camber and super elevation
Capacity

47. GRADE SEPARATED INTERSECTIONS
 In a grade separated intersection, the intersecting roadways
are placed at different elevations to allow uninterrupted
traffic movement.
 The grade separated intersections are classified as
OVERPASS and UNDERPASS.
 When the major highway is taken over the road of lesser
importance, it is called as OVERPASS.
 If the major highway is taken by depressing it below the
ground level to cross another road of less importance by
means of under bridge, it is known as UNDERPASS.

49. TRUMPET INTERSECTIONS

50. DIAMOND INTERCHANGE

51. PARTIAL CLOVER LEAF

52. CLOVER LEAF INTERCHANGE

53. ADVANTAGES OF GRADE
SEPARATION
It avoids necessity of stopping.
Avoids accidents at intersection.
There is increased safety or turning traffic.
There is overall increase in comfort and convenience to the
motorists and saving in travel time.
It is very useful for expressways.

54. DISADVANTAGES OF GRADE
SEPARATION
It is very costly.
Where there is limited right of way like built up or urban area
or where topography is not favourable, construction of grade
separation is costly, difficult and undesirable.

55. TYPES OF GRADE SEPARATED INTERSECTION
 Grade separated intersections without interchange.
 Grade separated intersections with interchange.
 Depending upon no of legs the intersection serves, they are classified
as-
 A) Three-legged Interchange
 T-Intersection
 Y-Intersection
 Partial rotary interchange
B) Four legged interchange
 Diamond Interchange
 Clover leaf interchange
 Rotary Interchange
 Directional Interchange
C) Multi-legged interchange
 Rotary interchange

56. ROTARY INTERCHANGE

57. DIRECTIONAL INTERCHANGE

58. TERMINAL FACILITIES
 Along the highway the terminal facilities required are:-
Bus stops
Bus bays
Drive ways
Footways