Road Junctions and Grade Separators for Transportation Planning - A Junction is an area, where two or more roads join or cross, whose main function is to provide for the change of route directions. Grade separation is a method developed to avoid the disruption of traffic flow at intersections. It is adopted at junctions where two or more surface transport axes cross with each other. Grade separation is generally achieved by means of a vertical level.

1. • ROAD JUNCTIONS
• GRADE SEPARATORS
• LOOP
• INTERCHANGE
• UNDERPASS
TRANSPORTATION
PLANNING
SUBMITTED BY :
SUBMITTED TO :
• Prachi Kothary – 6
• Akshata Parbate - 10
• Prof. Kishore Joglekar

2. ROAD JUNCTIONS
A Junction is an area, where two or more roads join or
cross, whose main function is to provide for the change
of route directions.
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• Since the main function of an intersection is to enable the road user to make a
route choice, it is a point of decision. Hence the problems that are
encountered by the motorist while passing through an intersection must be
recognized and the design should be in such a way that the driving task is as
simple as possible.
• Junctions tend to have a high potential for crashes.
COMPLEX JUNCTION
SIMPLE JUNCTION
ROAD JUNCTIONS
Only two roads crossing at
a right angle
Three or more roads cross
within the same area

3. TYPES OF INTERSECTIONS
Intersections are classified into two broad categories:
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GRADE SEPARATED INTERSECTION
INTERSECTIONS
INTERSECTION AT GRADE
• 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.
• An intersection is a junction where two or more roads meet or cross.
• Roads that cross each other at the same level or elevation are called
At Grade Intersections.

4. KEY ELEMENTS OF ROAD INTERSECTIONS
Intersection legs are those segments of roadway connecting to the intersection. The leg used
by traffic approaching the intersection is the approach leg, and that used by traffic leaving is
the departure leg.
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INTERSECTION LEGS
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Sidewalks, crosswalks, and pedestrian curb-cut ramps are considered to be within the
intersection. The pavement edge corner is the curve connecting the edges of the pavement of
the intersecting streets.
Channelizing and divisional islands may be added to an intersection to help delineate the area
in which vehicles can operate and to separate conflicting movements.
A turning roadway is a short segment of a roadway for a right turn, delineated by channelizing
islands.
Traffic control devices assign right of way, to both motorized and non‐motorized traffic and
include traffic signals, pavement markings, STOP signs, YIELD signs, pedestrian signal heads
and other devices.
SIDEWALKS | CROSSWALKS
ISLANDS
TURNING ROADWAY
TRAFFIC CONTROL DEVICES
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The key elements of Road Intersections can be
classified as follows :

5. INTERSECTIONS AT GRADE
THREE LEG
INTERSECTIONS
STAGGERED 4 LEG
INTERSECTIONS
ALIGNED 4 LEG INTERSECTION MULTI-LEG INTERSECTION
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T- Junction Skewed
Junction
Y - Junction
Staggered
Junction
Staggered–Skewed
Intersection
Cross
Intersection
Cross - Skewed
Intersection
5 - Leg
Intersection
6 - Leg
Intersection
Intersections at Grade are broadly classified into the following basic forms :

6. T - JUNCTION
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Y - JUNCTION
• T intersections work well in low and medium volumes of
traffic but can be difficult to emerge from when turning right
if traffic is heavy.
• The T-intersection must have traffic lights installed to
control when vehicles can go. When a stop sign is placed
at a T-intersection it is usually because visibility of the road
is restricted as you approach it.
• It is pretty useful in the distribution of traffic.
• To provide two options for vehicles traveling on
the main road.
A T-junction has three arms of which
one arm is a main road whereas the
other one is usually a minor road
connecting the main road.
A Y-junction has three arms of which
all three roads are of equal sizes. It is
generally seen in places of heavy
traffic.

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CROSS
JUNCTION
SKEWED -CROSS
JUNCTION
• Skewed cross junctions are often used when the
existing road layout or geographical constraints
make it impractical to have a standard
perpendicular intersection. This design helps to
optimize space and improve traffic flow.
• They can result in longer crossing distances for
pedestrians and facilitate higher-speed turning
movements by vehicles.
A four-way intersection, also known
as a crossroads, is where two roads
intersect each other at right angles,
forming a four-way junction.
• The purpose of Cross Junctions is to facilitate the
crossing of two perpendicular roads, allowing
vehicles to change their direction of travel.
• Crossroads are often used in urban and suburban
areas and can handle moderate to high traffic
volumes.
• Proper signalization and signage are crucial for
managing traffic efficiently.
A skewed cross-intersection is
similar to a crossroads, but the
roads do not intersect at right
angles; they are skewed or angled.

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STAGGERED
JUNCTION
SKEWED & STAGGERED
JUNCTION
• Typically, a minor road will meet a major road and
continue onto a minor road slightly further ahead.
• Major single-point traffic-light controlled junctions of
more than two roads are often reconfigured into
staggered junctions in order to increase traffic
flow through them.
• They are often used instead of a standard crossroad in
busy areas.
A skewed and staggered junction is a
combination of staggered and skewed
junctions where both the offset and the
non-right-angle elements are present.
A staggered junction is a place where several
roads meet a main road at a slight distance
apart thus they do not all come together at the
same point.
Purpose: This type of junction is often used in complex urban environments where space
constraints and irregular road layouts necessitate a combination of skewed and staggered
features to optimize traffic flow and safety.
Design: The design involves careful planning of the angle of intersection and the staggered
layout, taking into consideration traffic volume, turning movements, and pedestrian crossings.

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MULTI – LEG JUNCTION
SKEWED JUNCTION
A multi-leg junction refers to an intersection
with three or more roads converging at a
single point.
• Purpose: Multi-leg junctions are common in urban
areas with complex road networks. They are designed
to efficiently manage the flow of traffic from multiple
directions, including left and right turns.
• Design: The design of a multi-leg junction involves
considerations for traffic signals, turning lanes,
pedestrian crossings, and other features to ensure the
safe and smooth movement of vehicles from different
directions.
• This type of junction can be challenging for drivers
because of the skewed angle, which may require them to
make sharper turns or have limited visibility of oncoming
traffic.
• Warning signs are meant to improve safety by providing
advance notice to drivers and allowing them to adjust their
speed and approach accordingly.
A skewed side road junction refers to a
road intersection where one road meets
another at an angle instead of a typical
perpendicular intersection.

10. ROTARIES / ROUNDABOUT INTERSECTIONS
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Rotary intersections or roundabouts are special forms of at-grade intersections laid out for
the movement of Traffic in one direction around a central traffic island.
Essentially all the major conflicts at an intersection namely the collision between through and right-turn movements are
converted into milder conflicts namely merging and diverging.
• Traffic flow is regulated to only one direction of movement, thus eliminating severe
conflicts between crossing movements.
• All the vehicles entering the rotary are gently forced to reduce the speed and
continue to move at a slower speed.
• Because of the lower speed of negotiation and elimination of severe conflicts,
accidents, and their severity are much less in rotaries.
• Rotaries are self-governing and do not need practically any control by police or
traffic signals.
• They are ideally suited for moderate traffic, especially with irregular geometry, or
intersections with more than three or four approaches.
 ADVANTAGES OF ROTARY
Three types of conflicts when traffic streams
interfere with each other:
A. Merging
B. Diverging
C. Crossing

11. Diverging: It is a traffic operation when the vehicles moving in one
direction is separated into different streams according to their destinations.
Merging: Merging is the opposite of diverging. Merging is referred to as
the process of joining the traffic coming from different approaches and
going to a common destination into a single stream.
Weaving: Weaving is the combined movement of both merging and
diverging movements in the same direction.
These movements are shown in figure. It can be observed that movements
from each direction split into three; left, straight, and right turn.
DESIGN OF ROTARY
DESIGN ELEMENTS OF ROTARY
Design elements include design speed; entry, exit and central island radius; width of rotary; weaving length and
width; entry and exit widths.
TRAFFIC OPERATIONS IN ROTARY

12. ADVANTAGES OF GRADE SEPARATION
•Grade separation eliminates the stopping of vehicles
while crossing the roads.
•It provides safety and reduces the risk of accidents.
•Speed limits for grade-separated roads are generally higher
hence, high speeds can be maintained at intersections
which results in saving of travel time.
•Grade separation can be provided for all likely angles of any
two intersecting roads.
Grade separation is a method developed to avoid the
disruption of traffic flow at intersections. It is adopted at junctions
where two or more surface transport axes cross with each other.
Grade separation is generally achieved by means of a vertical level.
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The ultimate objective of grade-separated intersections (interchanges) is to eliminate all
grade-crossing conflicts and to accommodate other intersecting maneuvers by
merging, diverging, and weaving at low relative speed.
GRADE-SEPERATORS

13. 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 to cross over busy roads
without impacting traffic.
An underpass or a tunnel is an underground
passageway, completely enclosed except for
openings for ingress and egress, commonly at
each end. A tunnel may be for foot or vehicular
road traffic, for rail traffic, etc.
GRADE SEPARATION CAN BE ACHIEVED BY TWO INTERSECTIONS
OVERPASS UNDERPASS
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14. Grade separation eliminates intersection of traffic flow at junctions but it is
incomplete without provision for interchanges.
Interchanges facilitate the change of direction of traffic from one
highway to another highway at intersections.
Interchange ramps at grade separations can be provided in three different types
and they are :
INTERCHANGE
DIRECT SEMI-DIRECT INDIRECT
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MAJOR
INTERCHANGES
• Trumpet Interchange
• Diamond Interchange
• Cloverleaf Interchange
• Partial Cloverleaf
Interchange
• Directional Interchange
• Stack Interchange
• Rotary Interchange

15. KEY ELEMENTS OF INTERCHANGE
These are additional lanes on the main road specifically designated for vehicles entering or
exiting the interchange.
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ENTRY / EXIT LEGS
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These are inclined or curved sections of road that connect the main road to the interchange.
They can be on-ramps (for entering the interchange) or off-ramps (for exiting the interchange).
Bridges that allow one road to pass over another to eliminate intersections and facilitate
continuous traffic flow.
Distributor lanes or roads help manage local traffic within the interchange, providing access to
different ramps and facilitating smoother transitions.
A positive line is often painted on the road surface to indicate the correct path for vehicles to
follow, helping to prevent lane drifting and ensuring smooth traffic flow.
RAMPS
OVERPASS
DISTRIBUTOR LANE
POSITIVE LINE
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The key elements of Interchange can be classified
as follows :

16. • Ramps and Loops: Cloverleaf interchanges consist of a series of
ramps and loops that connect the intersecting highways. These ramps
form a pattern that allows vehicles to enter and exit the highways in a
smooth and efficient manner.
• Loop Ramps: The loop ramps in a cloverleaf interchange are
typically used for making left turns or U-turns. These ramps are
designed to loop around and pass over or under the intersecting
highways, allowing vehicles to change direction.
• Cloverleaf interchanges contain 4 legs and eight ramps.
• Cloverleaf interchanges are used at intersections where two major
highways cross each other.
• The objective of a cloverleaf is to allow two highways to cross
without the need for any traffic to be stopped by red lights, even for
the left and right turns.
Kathipara, Chennai
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CLOVER LEAF INTERCHANGE
A junction of two highways, one crossing over the other, having
a series of exit and entrance ramps, arranged in the form of a four-
leaf clover, such that traffic may proceed from either highway in
all directions.

17. • 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.
• A trumpet interchange is a type of
road junction that features a loop
ramp that turns 270 degrees,
resembling the shape of a trumpet. It
is often used when one road crosses
over another but there is not enough
space or the terrain is not suitable for a
full cloverleaf interchange.
Jamnagar-Amritsar Express highway
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A Trumpet interchange is a road junction that typically uses
grade separation, and one or more looped ramps, to permit traffic
on at least one highway to pass through the junction without
directly crossing any other traffic stream.
TRUMPET INTERCHANGE

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Two level semi-directional T interchange
in Orbe, Switzerland.
DIRECTIONAL INTERCHANGE
A directional interchange refers to a type of highway interchange designed to facilitate
the movement of traffic between two major roads or highways in a specific direction.
It allows vehicles to transition from one road to another in a smooth and efficient
manner. Directional interchanges are typically used in areas where two highways intersect,
and they aim to minimize disruptions to the flow of traffic.
• Directional interchanges are
generally preferred where two
high-volume freeways
intersect.
• They reduce travel distance,
increase ramp speed and
capacity, and eliminate
weaving movements.
• Since traffic movements
between the two freeways are
free-flow with this interchange
configuration, at-grade
intersections are eliminated, only
direct ramp connections from
one freeway to the other.

19. The High Five in Dallas, Texas. This is a complicated five-level
stack interchange, due to the proximity of frontage roads and
segregated high-occupancy vehicle lanes. This hybrid design is
based on parts of a four-level stack for highways, with a three-
level-diamond interchange to handle the frontage roads.
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A directional interchange, colloquially known as a stack interchange, is a
type of grade-separated junction between two access-controlled
highways that allows free entry and exit for traffic in all directions.
• These interchanges
eliminate weaving
problems, have the
highest vehicle capacity,
and offer shorter vehicle
travel distances
compared to other types
of interchanges.
• The first directional
interchange built in the
world was the Four Level
Interchange, which opened
to Los Angeles Transit in
1949.
STACK INTERCHANGE

20. The first DI in Washington State was
built at the Interstate 5 and State Route
510 (Marvin Rd) interchange in Lacey,
WA.
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A diamond interchange is a common type of road junction,
used where a controlled-access highway crosses a minor road.
• Visual showing how diamond
interchanges are used, with an
expressway running across and a
local road running in the center.
• The freeway itself is grade-
separated from the minor road, one
crossing the other over a bridge.
Approaching the interchange from
either direction, an off-ramp
diverges only slightly from the
freeway and runs directly across the
minor road, becoming an on-ramp
that returns to the freeway in similar
fashion.
DIAMOND INTERCHANGE

21. Highway 407 Electronic Toll Route in Ontario
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PARTIAL CLOVERLEAF
Partial cloverleaf is a modification that combines some
elements of a diamond interchange with one or more loops of a
cloverleaf to eliminate only the more critical turning conflicts. It
provides more acceleration and deceleration space on the
freeway.
• The Diamond Interchange has four
ramps.
• The Cloverleaf Interchange has eight
ramps like the Stack Interchange.
• Unlike Parclos, it is completely sterically
separated and traffic flows without stopping
on all ramps and main roads.
• Parclos usually have 4 or 6 ramps, but
rarely 5 ramps.
• Partial cloverleaf interchanges are often
used in situations where a full cloverleaf
interchange is not feasible due to space
constraints, cost considerations, or
other limitations. They provide a balance
between the efficiency of a cloverleaf
design and the constraints of the
surrounding environment.

22. 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
roads
without
impacting
traffic.
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ROTARY INTERCHANGE
A Rotary interchange is typical to enter a rotary alongside traffic that
is circulating in the inside lanes, like a freeway cloverleaf loop entrance
where the ramp entrance lane continues under or over a bridge to the next
exit.
• A rotary interchange, also known as a roundabout or
traffic circle, is a type of road junction in which traffic
moves in one direction around a central island.
• In a rotary interchange, vehicles enter the circle at
various points and navigate around it until they
reach their desired exit, which could be a specific
road leading away from the circle.
• The circular design helps to eliminate the need for traffic
signals and allows for a more continuous flow of
vehicles. Drivers entering a rotary interchange must
yield to the circulating traffic before merging into the
circle.
• Rotary interchanges are common in many countries
around the world and are considered an effective
traffic management solution when designed and
implemented appropriately.
Rotary interchange in Italy.

23. CONCLUSION
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• In closing, the intricate dance of roads converging at a junction symbolizes the interconnected pathways of our transportation
networks.
• Navigating through these intersections requires a harmonious blend of careful planning, innovative design, and advanced
technology.
• As we conclude our exploration of road junctions, let us remember that these intersections serve as the crossroads of progress,
enabling the smooth flow of people and goods, fostering economic growth, and connecting communities.
• Just as roads converge at a junction, so do the various elements of urban planning, engineering, and technology converge to create
a safer, more efficient, and sustainable transportation infrastructure.
• Let us continue to invest in the future of road design, embracing new ideas and solutions that pave the way for a connected and
vibrant world.