This document discusses different types of road intersections and design considerations. It describes two main types of intersections - grade-separated, which use overpasses or underpasses to eliminate conflicts, and at-grade intersections. Some key intersection types are described, including diamond, cloverleaf, and directional interchanges. Design elements like capacity, traffic control, and accommodation of pedestrians and bicycles are also covered. The objective of grade-separated intersections is to eliminate conflicts while accommodating turning movements. Channelization is discussed as a way to reduce the conflict area at intersections.

1. By
G. Sowjanya

2.  Intersection is an area shared by two or more
roads.
 This area is designated for the vehicles to
turn to different directions to reach their
desired destinations.
 This is because vehicles moving in different
direction want to occupy same space at the
same time.

3.  There are two main types of intersection of
roads.
 Grade – separated intersections or
interchanges.
 At – grade intersections.

4.  It is a bridge that eliminates crossing conflicts at
intersections by vertical separation of roadways in
space.
 Route transfer at grade separations is accommodated
by interchange facilities consisting of ramps.
 The interchange configurations are designed in such
a way to accommodate economically the traffic
requirements of flow, operation on the crossing
facilities, physical requirements of the topography,
adjoining land use, type of controls, right-of-way and
direction of movements.

5. Objective:
 The ultimate objective of grade separated
intersections is to eliminate all grade crossing
conflicts and to accommodate other
intersecting maneuvers by merging, diverging
and weaving at low relative seed.

6.  One of the distinctions made in type of
interchange is between the directional and
the non directional.
 Directional interchanges are those having
ramps that tend to follow the natural
direction of movement.
 Non directional interchanges require a
change in the natural path of traffic flow.

7.  Underpass
 Overpass
 Trumpet Interchange
 Diamond Interchange
 Cloverleaf Interchange
 Partial cloverleaf Interchange
 Directional Interchange
 Bridged Rotary

8.  An underpass or a tunnel is an underground
passageway, completely enclosed expect for
openings for ingress and egress, commonly
at each end.
 A tunnel may be for foot or vehicular road
traffic, for rail traffic.

10.  An overpass also known as a flyover, is a
bridge, road, railway or similar structure that
crosses over another road or railway.
 A pedestrian overpass allows pedestrians safe
crossing over busy without impacting traffic.

12.  Trumpet interchanges have been used where
one highway terminates at another highway.
 These involve at least one loop ramp connecting
traffic either entering or leaving the terminating
expressway with the far lanes of the continuous
highway.
 The principal advantages are low construction
cost and are useful for highways as well as toll
roads.

14.  A diamond interchange is a common type of
road junction, used where a freeway crosses a
minor road.
 The diamond interchange uses less space
than most types of freeway interchange, and
avoids the interweaving traffic flows that
occur in interchanges such as the cloverleaf.
 Diamond interchanges are most effective in
areas where traffic is light.

16.  A cloverleaf interchange is a two-level
interchange in which left turns are handled by
ramp roads.
 To go left(in right-hand traffic), vehicles first
continue as one road passes over or under
the other, then exit right onto a one-way
three-fourths loop ramp (270) and merge
onto the intersecting road.

18.  Partial clover leaf is a modification that
combines some elements of a diamond
interchange with one or more lops of a
cloverleaf to eliminate only the more critical
turning conflicts.
 It provides more acceleration and
deceleration space on the freeway.

20.  A Directional interchange provides direct for left
turns.
 These interchanges contain ramps for one or
more direct or semi direct left turning
movements.
 Interchanges of two freeways or interchanges
with one or more very heavy turning movements
usually warrant direct ramps, which have higher
speeds of operation and higher capacities,
compared to loop ramps.

22.  At-grade intersections in which all the
exchanges between the roads take place on
the sane plane.
 These are of two types
 Standard at-grade intersections
 Round about at-grade intersections.

26.  Simple intersections maintain the street’s
typical cross-section and number of lanes
throughout the intersection, on both the
major and minor streets.
 Simple intersections are best-suited to
locations where auxiliary (turning) lanes are
not needed to achieve the desired level-of-
service.

28.  Vehicles approaching an intersection are directed to
definite paths by islands, marking etc. and this
method of control is called channelization.
 Channelized intersection provides more safety and
efficiency.
 It reduces the number of possible conflicts by
reducing the area of conflicts available in the
carriageway.
 If no channelizing is provided the driver will have less
tendency to reduce the speed while entering the
intersection from the carriageway.

30. Design parameters of
intersections

31.  Crossings and pedestrian curb cut Ramp
Locations
 Walking Speed
 Pedestrian Flow Capacity
 Traffic Control, Yielding and Delay

32.  Cross-section- Bicyclists position themselves
for their intended destination regardless of
the presence of bike lanes or shoulders.
 Operating Speed- At un signalized
intersections, an average bicycle speed of 15
miles per hour can be assumed on the major
project.

33.  Bicycle Capacity - The number of bicycles
per hour that can be accommodated by the
facility under normal conditions.
 Traffic Control - Bicyclists are required by
law to obey control devices at intersections.
Therefore, traffic control devices need to
account for bicycle activity.

34. Design Vehicle
*The largest type of motor vehicle that is normally
expected to be accommodated through the intersection.
*At intersections, the most important attribute of design
vehicles is their turning radius, which in turn influences
the pavement corner radius and therefore the size of the
intersection.
*Lane width, another feature related to the design vehicle,
has some impact on intersection design.
* The design vehicle appropriate for most types of transit
service is the “city-Bus” as defined by AASHTO.

36. Passive control
> No control
> Traffic signs
> Traffic signs plus marking.

37. Semi control
 Channelization
 Traffic rotaries
Active control
 Traffic signals
 Grade separated intersections

41.  Intersection area is paved and there is absolutely
no restriction to vehicles to use any part of
intersection area.
 Hence the un channelized (all-paved) intersections
are the lowest class of intersection, easiest in the
design but most complex in traffic operations
 Resulting in maximum conflict area and more
number of accidents, unless controlled by traffic
signals or police.

42.  Plain intersection:
No provision for
additional pavement
width for turning
movements
 Flared intersection:
Provision for additional
pavement width for
turning movements

43.  A small raised area in the middle of a road which
provides a safe place for pedestrians to stand
and marks a division between two opposing
streams of traffic.
(or)
 A traffic island is a solid or painted object in a
road that channelizes traffic. It can also be a
narrow strip of island between roads that
intersect at an acute angle.
 If the island uses road markings only, without
raised kerbs or other physical obstructions, it is
called a painted island. Traffic islands can be
used to reduce the speed of vehicles driving
through.

44.  Divisional Islands: Divisional islands are dividing the
highway in two one way road way so that head on
collision are eliminated and accidents are reduced.
 Channelizing Islands: Channelizing islands guide the
traffic into proper channel through the intersection
area.
 Pedestrian loading Islands: They are provided at
regular bus stops and similar laces for the protection of
passengers.
 Rotary Islands: Rotary islands is the large central
island of a rotary intersection.

45.  Rotary intersections or
round abouts are special
form of at-grade
intersections laid out for
the movement of traffic
in one direction around a
central traffic island.
 The vehicles entering the
rotary are gently forced
to move in a clockwise
direction in orderly
fashion.

47.  IRC suggest that a two-lane of 7m width should be
kept as 7m for urban roads and 6.5 for rural roads.
Further for a three-lane road ofb10.5m is to be reduced
to 7m and 7.5m respectively for urban and rural roads.
 The width of weaving section should be higher than the
width at entry and exit. The weaving with is given as,
Where e1 = width of carriageway at the entry
e2 = width of carriageway at the exit
W weaving= {(e1+e2)/2} +3.5 m

48.  The capacity of rotary is determined by the capacity of
each weaving section. Transportation road research lab
(TRL) proposed the following empirical formula to find
the capacity of the weaving section.
 where is the average entry and exit width, is the
weaving width, is the length of weaving, and is the
proportion of weaving traffic to the non-weaving traffic.
 four types of movements at a weaving section, and are
the non-weaving traffic and are the weaving traffic.

49.  “Determine the radius of a circle in which
lengths of two chords ‘a’ and ‘b’ are known
and the chords meet at any point on the
periphery of the circle” ?..
 The equation derived as solution of the
problem is given below. It is a quadratic
equation in terms of R2.

50. i. Length of Intersecting straights with minimum site
distances recommended by I.R.C. are: 50 km/h.,
ii. Minimum Sight distance 15 m along minor roads S.K.
Mahajan et al. / Procedia - Social and Behavioral
Sciences 96 ( 2013 ) 2791 – 2799 2795
iii. Weaving Distance = 110 m, 145 m, 180 m and 220 m
for speeds 50 km/h., 65 km/h., 80 km/h, 100 km/h.
respectively. Minimum Weaving length: 30 to 50 m
iv. All traffic islands are constructed 200 mm higher than
road level. They are provided with lawn, statue or
fountains, painted with colours in contrast with the
road pavement.
{1-(a/b)2} R4-{b2-5a2/4} R2 –(a2b2/2) = 0