This document discusses junction design and traffic engineering. It defines different types of junctions including intersections and interchanges. Factors that affect junction loads are discussed. The types of movements at junctions like turning, merging, and diverging are also outlined. Conflict points and areas at intersections are explained. Methods to reduce conflicts at four-leg junctions using techniques like channelization are presented. Selection factors for junction types and different types of sight distances at junctions are also summarized. Finally, traffic light design and terminology used in traffic light phasing are covered.

1. CHAPTER 3.0
JUNCTION DESIGN
CC503 – TRAFFIC ENGINEERING

2. JUNCTION
• A road junction is a
location where
vehicular traffic going in
different directions can
proceed in a controlled
manner designed to
minimize accidents.
• In some cases, vehicles
can change between
different routes or
directions of travel.

3. INTERSECTION
• An intersection is a
road junction where
two or more
roads either meet or
cross at grade (they are
at the same level).
• Such a road junction
may also be called a
crossroads.

4. FACTORS THAT AFFECT JUNCTION
LOAD.
• At grade intersections
present a driver with
several points of
conflict with other
vehicles.
• The aims of
intersection design
are to improve traffic
flow and reduce the
like hood of accidents.

5. FACTORS THAT AFFECT JUNCTION
LOAD.
• Factors that affect junction load are:-
i. Geometrical design and traffic control devices
ii. Total or length wide
iii. Distribution design
iv. Turning radius
v. Traffic volume and characteristic

6. TYPE OF JUNCTION
AT GRADE JUNCTION
• Junction without signage/control
• Priority Junction
• Priority Junction with routing
• Roundabout with or without traffic light
• Traffic light controlled junction
• Tiered junction
GRADE SEPARATED OR INTERCHANGED
• Trumpet interchange:
• Diamond interchange:
• Clover leaf interchange

7. Junction without signage/control

8. Priority Junction

9. Priority Junction with routing

10. Roundabout with or without
traffic light

11. Traffic light controlled junction

12. Tiered junction

13. DIAGRAM TO DETERMINE INTERSECTION TYPE
(ARAHAN TEKNIK JALAN 11/87)

14. Trumpet Interchange

15. Diamond interchange

16. Cloverleaf Interchange

17. TYPES OF
MOVEMENTS AT
THE JUNCTION
a. Turning
b. Intersect
a. Turning
b. Intersect/cr
ossing
c. Link/merge
d. Diverges
e. weaves

18. • Link / merge

19. • Diverges

20. • Weave

21. CONFLICT POINT AND CONFLICT AREA
AT AN INTERSECTION
• Conflict points are commonly used to explain the
accident potential of a roadway.
• Access management strategies are typically
designed to reduce the number and density of
conflict points.
• A conflict point is the point at which a highway
user crossing, merging with, or diverging from a
road or driveway conflicts with another highway
user using the same road or driveway

22. CONFLICT POINT AND CONFLICT AREA
AT AN INTERSECTION
Here, how conflict happen:-
• Vehicles travel from two streams and meets
with each other
• Where roads cross at an acute angle or the
opposing legs of an intersection are offset,
excessive intersection area results
• In general, large areas of uncontrolled
pavement invite dangerous vehicle maneuvers
and should be eliminated

23. CONFLICT POINT AND CONFLICT AREA
AT AN INTERSECTION
Total
Junction
Intersect
Conflict
Link
Conflict
Diverge
Conflict
Total
Conflicts
3 3 3 3 9
4 16 8 8 32
5 49 15 15 79
6 124 24 24 172

24. • Figure 1.0: Conflict at 4 legs-junction and No
right turn method to solve conflict
6 link conflicts
8 Intersect conflicts
6 diverge conflicts

26. SKETCH THE METHOD TO REDUCE CONFLICT AT
4-LEG JUNCTION BELOW:-
1. No right turn
2. One of the road become one way movement
3. Both road become one way movement
4. Change 4 leg cross section become staggered
intersection
5. Use channelized

27. ANSWER OF METHOD TO
REDUCE CONFLICT AT JUNCTION

28. One of the road become one way
movement
7 Intersects
2 Diverges
2 Merges

29. Both road become one way movement
4 Intersects
2 Diverges
2 Merges

30. Change 4 leg cross section become
staggered intersection
6 Intersects
6 Merges
6 Diverges

31. Use Channelization
• Channelization of traffic
through a three-legged
intersection
• Channelization of traffic
through a four-legged
intersection

32. SELECTION FACTORS OF JUNCTION
TYPE:-
i. Volume, composition and speed of traffic in each
stream
ii. Hierarchy of roads that intersect with each other
iii. Clarity of vision in different weather condition
iv. Type and rate of control of traffic entering
v. Area and the cost of land use
vi. Total conflict at intersection
vii. Construction and maintenance cost
viii. Accident data (to be used for intersection’s planning)

33. TYPE OF SIGHT DISTANCE AT JUNCTION
A. Sight triangle
B. Sight distance for approach
• No Stop or Signal Control at Intersection
• Signalized intersection
• Stop controlled intersection
C. Sight distance for departure

34. TYPE OF SIGHT DISTANCE AT JUNCTION
Figure 2.1: Intersection Sight Triangle

35. TYPE OF SIGHT DISTANCE AT JUNCTION
Figure 2.2: No Stop or Signal Control at Intersection

36. TYPE OF SIGHT DISTANCE AT JUNCTION
Figure 2.3: Stop Control on Minor Road

37. SIGNALIZED INTERSECTION
• The sight distance is the sum of a distance travelled
during the total reaction time which is the interval
between the instant that the driver recognizes the
traffic signals of the intersection ahead and the instant
that the driver actually applies the brakes, and a
distance to stop the vehicle at the stop line with
applying brake.
S = (Vt/3.6) + [ (1/2)*(V/3.6)2 ]
Where, t = 10 sec. (rural), t = 6 sec (urban),
 = 0.2 x g = 0.2 x 9.8 = 1.96 m/sec2

38. STOP CONTROLLED INTERSECTION
• In this case, time for decision making as in
signalized intersection is not necessary
because every driver must stop.
S = (Vt/3.6) + [ (1/2)*(V/3.6)2 ]
Where, V= speed (km/h), t = 2 sec,
 = 1.96 m/sec2

39. SIGHT DISTANCE FOR DEPARTURE
• At an intersection where traffic is controlled by STOP signs
on the minor road it is necessary for the driver of a stopped
vehicle to see enough of the major road to be able to cross
before a vehicle on the major road reaches the intersection
d = 0.28V (J + ta)
Where,
d = minimum sight distance along the major road from the intersection,
meters.
V = design speed of major road, km/hr.
J = sum of perception time and the time required to shift to first gear or
actuate an automatic shift. (Assume J = 2 sec, Urban or sub-urban = 1 ½
sec to 1 sec))
ta = time required to accelerate and traverse the distance S to clear the major
road, seconds.

40. SIGHT DISTANCE FOR DEPARTURE
S = D + W+ L
Where,
S = Distance for vehicle must travel to cross the major road
D = distance from near edge of pavement of front of stopped vehicle
W= width of pavement along path of crossing vehicle.
L = overall length of vehicle

41. Example
• A vehicle travel before hit to collision point has 2
sec of reaction time to stop, deceleration of
vehicle is 1.96 m/s2 and the speed of vehicle is
100 km/hr. Determine the sight distance for a
vehicle before it hit the collision point.
Solution
S = (Vt/3.6) + [ (1/2)*(V/3.6)2 ]
= (100 x 2)/3.6 + [(1/2 x 1.96) x (100/3.6)2]
= 252.4 m

43. TRAFFIC LIGHT DESIGN AND PHASES
• Traffic lights which may also be
known as stoplights, traffic
lamps, traffic signals, stop-and-
go lights, robots or semaphore,
are signaling devices positioned
at road intersections,
pedestrian crossings and other
locations to control competing
flows of traffic.

44. ADVANTAGES & DISADVANTAGES TRAFFIC LIGHT
ADVANTAGES
i. Provide orderly movement of
traffic
ii. Minimize the number of
conflicting movements
iii. Increase capacity
iv. Interrupt heavy traffic to
allow other traffic to enter or
cross.
v. Coordinated continuous
movement of traffic at a
desired speed
vi. Promote driver confidence
DISADVANTAGES
i. Increase total intersection
delay especially during off
peak periods
ii. Probable increase in certain
types of accidents
iii. Interrupt the progressive
flow of traffic on a route
cause delay & stopping
iv. When improperly located
causes unnecessary delay
v. When improperly timed,
causes excessive delay,
increasing driver irritation

45. REQUIREMENT OF TRAFFIC
INSTRALLATION
• THREE (3) warrant should be
considered before installing traffic
signal are:-
 Warrant 1: Vehicular Operations
 Warrant 2: Pedestrian Safety (S)
 Warrant 3: Accident Experience

46. PHASING ELEMENTS
• Definition:
A signal phase is a part of the cycle length
allocated to a traffic movement receiving the
right of way simultaneously during one or more
intervals
• A traffic movement is a single vehicular
movement, a single pedestrian movement, or a
combination of vehicular and pedestrian
movements
• Cycle length = the sum of all traffic phases

47. TYPE OF PHASING
N-S: Red N-S: Green (all movements)
E-W: Green (all movements) E-W: Red

48. N-S:Red N-S: Red N-S: Green (all movements)
E-W:Green(TM) E-W: Red (TM) E-W: Red
: Red (RT) : Green (RT)

50. TRAFFIC LIGHT TERM
1. LOST TIME, L
 It indicates the time during which the intersection
is not effectively utilized for any movement.
2. INTERGREEN PERIOD OR INTERVAL, I
 Intergreen period is defined as the period
between one phase losing right of way and the
next phase gaining right of way, or the time
between the end of green on one phase and the
start of green on the next.

51. TRAFFIC LIGHT TERM
3. ACTUAL GREEN TIME, GT
 The time within a cycle in which an approach has the
green indication (express in second and symbol GT).
4. EFFECTIVE GREEN, g
 Effective green defined as the length of time that
would be required to get a given discharge rate over
the stop-line if the flow commenced and finished
simultaneously and instantaneously on the change of
colour as displayed on the signal head
 Formula: g = Co – L

52. TRAFFIC LIGHT TERM
5. RED TIME, RT
 The time within a cycle in which an approach has
the red indication (express in second and symbol
RT).
6. AMBER OR YELLOW TIME, a
 The time within a cycle in which an approach has
the yellow indication (express in second and
symbol a)

53. TRAFFIC LIGHT TERM
7. CYCLE LENGTH, C
 One complete sequence ( for all approaches of
signal indications [green, yellow, red] ).
 Cycle time maximum (Cm) is 120 second (2
minutes) is considered as good practice.
Normally, the cycle time will lie within the range
of 30 – 90 s.