10-Intersection Control ( Transportation and Traffic Engineering Dr. Sheriff El-Badawy )

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‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
Traffic Control Devices
• Broad Category of Traffic Control Devices:
• Traffic Marking
• Traffic Signs
• Traffic Signals
• To be effective, a device must:
1. Fulfil a specific purpose
2. Command attention
3. Convey a clear simple meaning
4. Command respect of road users
5. Give adequate time for proper response
Traffic Markings
• Longitudinal Markings:
• Yellow line delineate the separation of opposing traffic flows
• White line marks right edge of pavement
• Broken lines are permissive
• Solid lines are restrictive
• Double lines indicate maximum restriction
• Markings must be visible at night

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Longitudinal Marking
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Yellow Line = Two-way Traffic
White Line = One-way Traffic
Solid Line = No Passing
Broken Line – Pass with Caution
Traffic Flow
Traffic Flow
Two way traffic no
passing
Two way traffic pass
with caution
Yellow Line
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Traffic Flow
Traffic Flow
White Lines
No passing - solid line
One-way traffic
Broken - pass with caution
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ONE WAY – pass
with caution
TWO WAY – no passing
over solid lines
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Multi-Lane

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Traffic Markings
• Transverse Markings:
• Placed across travel lanes
• Stop line: Solid white lines required in urban and rural areas
• Crosswalks: Number of different ways to mark crosswalks
• Parking Lanes: Not mandatory, but improves the efficiency
Stop line
Traffic Marking
• Word/ Symbol Markings

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1. Regulate traffic, movement or parking
2. Warn of potential dangers or road conditions
3. Provide information and guidance
Traffic signs have three purposes
Traffic Signs
• Regulatory Signs: Convey information on specific traffic
regulation, drivers must comply
– Right-of-way series, Speed series
– Movement series (turn signs, alignment signs, exclusion signs,
one-way signs)
– Pedestrian series, Parking series, Miscellaneous
• Warning Signs: Provides information on impending condition
that may be or are hazardous
– Changing in horizontal alignment, Intersections and grades,
Advance warning for control devices, Converging traffic lanes,
Narrow roadways, Changes in highway design, Roadway
surface conditions, Railroad crossings,
– Entrances and crossings

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Traffic Signs
• Guide Signs: Provides information on selecting appropriate
routes
• Utmost important for driver’s safety
• Route Markers, Destination Signs: Conventional roadways,
• Destination Signs: Motorways, Service Guide signs, Mileposts
Colors Have Meaning
Red Green
Blue Yellow
Black White
Orange Brown
Fluorescent Optic Yellow

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Shapes Have Meaning
Octagon Rectangle
Triangle
Diamond
Pentagon
Pennant
Rectangle
Circle
Crossbuck
Three Types of Signs
Regulatory
Warning
Guide

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Where must drivers stop?
Where are they located?
When must drivers yield?
Where are they located?

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SPEED LIMIT SIGNS
Speed Limits
 Urban Areas
 Parks
 Rural Interstate
 Urban Interstate
 School Zones

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RR sign or RR painted
on the pavement are
advanced warning
signs.
Crossbucks are yield signs.
The train has the right-of-way!
Railroad Crossing Warnings
Flashing red lights
Bells
Gates
If you hear or see a train
Other Regulatory Signs

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ORANGE is for Construction
REMEMBER
 Common Sense
 Caution
 Concentration
Markings Indicating Drivers are
Entering a Work Zone

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Work Zones Areas
Advance
Warning
Transition
Buffer
Work
Area
E
N
D
GUIDE SIGNS
US Route Marker

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Intersections
An intersection is the general area where two or more highways
join or cross.
It includes the areas needed for all modes of travel:
• pedestrian,
• bicycle,
• motor vehicle,
• and transit.
Intersections are an important part of a highway facility because
their design affect greatly:
• Efficiency,
• Safety,
• Cost of operation, and
• Capacity of the facility.

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Intersection Types
Grade separated
At-grade
With ramps
(Interchanges)
Without ramps
(meaning no
connection
between the
intersection
roads!)
At-Grade Intersection
Source: FHWA Flexibility in Highway Design

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2)Grade Separation without Ramps
3) Interchanges

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Interchanges
Utilize grade separation
Additional illustrations at
http://www.kurumi.com/roads/
interchanges/index.html
Intersection Design
• Reduce conflicts between road users
• Improve efficiency and safety
• Consider:
• Human factors
• Traffic
• Geometrics
• Economics

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Intersection Types
Basic intersections are
• Three-leg (or T),
• Four leg, and
• Multi-leg intersections.
Three-Leg Intersections
• The angle of intersection is formed by the intersecting
streets centerlines.
• The best angle is between 75 and 105 degrees.

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Four-Leg Intersections
• The angle of intersection is formed by the intersecting
streets centerlines.
• The best angle is between 75 and 105 degrees.
Multi-Leg Intersections

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Basic Types of Movements within
Intersections
• Crossing
• Merging
• Diverging
• Weaving
Crossing
• Direct Crossings: angle of skew 75 to 105 degrees,
• Oblique Crossing: angle of skew below 75 or above
105 degrees.
• Oblique skews should be voided if at all possible.

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Merging
(Joining Traffic Stream)
Diverging
(Separating from Traffic Stream)
Weaving
Weaving is the combined movement of both merging and
diverging movements in the same direction.

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Conflict Points at 4-Leg Intersections
Conflict Points at T Intersection

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Conflict Points
Cross Intersection Versus Roundabout

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Sight Triangle
Intersection Sight Triangle
Hidden Vehicle

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Intersections
• Intersections are a key feature of street design in four respects:
• Focus of activity - The land near intersections often contains a
concentration of travel destinations.
• Conflicting movements - Pedestrian crossings, vehicle and
bicycle turning and crossing movements are typically concentrated
at intersections.
• Traffic control - At intersections, movement of users is assigned by
traffic control devices such as yield signs, stop signs, and traffic
signals. For this intersections are often major cause of delay, but
helps to organize traffic and reduce the potential for conflicts.
• Capacity - In many cases, traffic control at intersections limits the
capacity of the intersecting roadways which is defined as the
number of vehicles that can be accommodated within a given period
of time.

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Intersection: Key Elements
Key Elements (1)
• The major street is typically the intersecting street with greater traffic
volume, larger cross-section, and higher functional class. The minor
street is the intersecting street likely to have less traffic volume,
smaller cross-section and lower functional classification than the
major street.
• Intersection legs are those segments of roadway adjacent 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.
• Sidewalks, crosswalks and pedestrian curb cut ramps are
considered to be within the intersection. The pavement corner is the
curve connecting the edges of pavement of the intersecting streets.
• The angle of intersection is formed by the intersecting streets’
centrelines. If the angle departs significantly from right angles, the
intersection is called skewed intersection
• Auxiliary lanes are lanes added at the intersection, usually to
accommodate turning motor vehicles. They may also be used to add through
lanes through an intersection.

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Key Elements (2)
• 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. Islands can also provide for
pedestrian refuge.
• A turning roadway is a short segment of roadway for a right turn,
delineated by channelizing islands. Turning roadways are used where
right-turn volumes are very high, or where skewed intersections would
otherwise create a very large pavement area.
• 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
•
Intersections
The functional area of an
intersection includes any
auxiliary lanes and their
associated channelization.

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Elements of the Functional Area of an Intersection
The functional area on the approach to an intersection or
driveway consists of three basic elements:
(1) Perception-reaction distance,
(2) Maneuver distance, and
(3) Queue-storage distance.
Functional of Impact Length
Maneuver Distance
Decision
Distance
Stopping Queue
or Storage
length
Begin
Deceleration
Begin
Perception Reaction
Deceleration
Completed
At-Grade Intersection Design
Objectives and Considerations
Need to meet two conflicting objectives:
Minimize the severity of potential conflicts among different
streams of traffic and between pedestrians and turning vehicles.
Provide for the smooth flow of traffic across the intersection
Operating
characteristics of
both the vehicles
and pedestrians
Adequate pavement
width and approach
sight distances must be
provided.

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BASIC DESIGN PRINCPLES
T - Intersections
• Suitable for minor or local roads.
• May be used when minor roads
intersect important highways with
an intersection angle less than 30
degrees from the normal.
• Also suitable for use in rural two-
lane highways that carry light
traffic.
• At locations with higher speeds
and turning volumes, which
increase the potential of rear-end
collisions between through
vehicles and turning vehicles.
• Usually an additional area of
surfacing or flaring is provided.

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T - Intersections
Provide auxiliary lane:
in cases where left-turn
volume from a through
road onto a minor road
is sufficiently high but
does not require a
separate left-turn lane.
Auxiliary
Lane
• Channelized T intersection
in which the two-lane
through road has been
converted into a divided
highway through the
intersection.
• Intersection of this type
probably will be signalized.
Channelization: Objectives
• Direct the paths of
vehicles
• Control the merging,
diverging, and crossing
angle of vehicles
• Reduce the amount of
paved area
• Provide a clear indication
of the proper path for
different movements
• Give priority to the
predominant movements
• Provide pedestrian refuge
• Provide separate storage
lanes for turning vehicles
• Provide space for traffic
control devices for
visibility
• Control prohibited turns
• Separate different traffic
movements at signalized
intersections with multiple-
phase signals
• Restrict the speeds of
vehicles

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4-Leg Intersections
• Mainly used at locations
where minor or local roads
cross.
• it also can be used where a
minor road crosses a major
highway.
• In these cases, the turning
volumes are usually low and
the roads intersect at an
angle that is not greater
than 30 degrees from the
normal.
Simple Unchannelized Intersection
4-Leg Intersections
• Right-turning roadways are
provided when right-turning
movements are frequent.
• Also common where
pedestrians are present.
Right
Turning
Roadways

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4-Leg Intersections
Suitable for:
• A two lane highway
• Not a minor crossroad.
• Carries moderate volumes at high speeds
• or operates near capacity.
4-Leg Intersections (Channelized)
Suitable for:
• Four lane approaches
• Carrying high through volumes and high turning volumes.
• Usually signalized

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• Multi-leg intersections have five or more approaches.
• Whenever possible, this type of intersection should be avoided.
In order to remove some of the conflicting movements and increase
safety and operation one or more of the legs are realigned.
Note: the distances between the aligned
intersections should be great enough to
allow for the independent operation of
each intersection.

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Intersection Control

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Intersection Control
• The purpose of traffic control is to assign the
right of way to drivers.
• Thus to facilitate highway safety by ensuring
the orderly and predictable movement of all
traffic on highways.
• Control may be achieved by:
• Traffic signals,
• Signs,
• Markings
Traffic Signals
• One of the most effective ways of controlling
traffic at an intersection.
• Improve overall safety by eliminating many
conflicts.
• Decrease average travel time and increase
capacity through an intersection
• Equalize the quality of service for all or most
traffic streams

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Traffic Signal
• Separate individual movements in time
rather than in space
Terminology & Definitions
• Green time: The time period in which the traffic signal has the green
indication
• Red time: The time period in which the traffic signal has the red indication
• Yellow time: The time period in which the traffic signal has the yellow
indication
• Cycle: One complete rotation or sequence of all signal indications
• Cycle time (or cycle length): The total time for the signal to complete
one sequence of signal indication.

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• Lost Time: A portion of green or yellow time which is not utilised
by traffic flow movements in a cycle.
• Start-up lost time (l1): At the beginning of each green indication
as the first few cars in a standing queue experience start-up
delays. This delay is measured as start-up lost time.
• The clearance lost time (all-red): It is estimated by the amount
of the yellow time not used by vehicles.
• Phase: That part of a cycle allocated to a stream of traffic or a
combination of two or more streams of traffic having the right-of-
way simultaneously during one or more intervals.
• Effective green time (gi): The effective green time, for a phase,
is the time during which vehicles are actually discharging
through the intersection,
Gi = actual green time, Yi = yellow time, tL = lost times for a phase i.
Terminology (Cont’d)
Terminology (Cont’d)
• All-red interval. The display time of a red
indication for all approaches.
• It is sometimes used as a phase exclusively
for pedestrian crossing or to allow vehicles
and pedestrians to clear very large
intersections before opposing approaches are
given the green indication.

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Two Phase Signal System
Traffic Signal Times9
0

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Saturation Flow
Number of vehicles that would pass through
the intersection during an entire hour of green
G
Time (sec)
FlowRate(vphpl)
Y
Saturation
Flow S
Given h, S=?
Effective Green Time
Effective Green G’
G
Time (sec)
FlowRate(vphgpl)
Y
Saturation
Flow
Time during which the flow is assumed to take
place at saturation flow

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Lost Time
Effective Green G’
G
Time (sec)
FlowRate(vphgpl)
Y
Saturation
Flow
Time during which no flow takes
place
Lost Time
I2
Lost Time
I1
  21 llGYG 
Discharge Headways
• Consider N vehicles discharging from the intersection
when a green indication is received.
• The first discharge headway is the time between the
initiation of the green indication and the rear wheels of
the first vehicle to cross over the stop line.
• The Nth discharge headway (N>1) is the time between
the rear wheels of the N-1th and Nth vehicles crossing
over the stop line.

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Discharge Headways
• The headway begins to level off with 4 or 5th vehicle.
• The level headway = saturation headway
• Start-up lost time can be expressed as: 1 ( )l e i 
Saturation flow rate
In a given lane, if every vehicle consumes an
average of h seconds of green time, and if the signal
continues to be uninterruptedly green, then S vph
could enter the intersection where S is the
saturation flow rate (vehicles per hour of green time
per lane) given by
3600
S
h


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Intersection Capacity
The maximum hourly rate at which persons or vehicles can
be reasonably expected to traverse a point or uniform
segment of a lane or roadway during a given time period
under prevailing traffic and roadway conditions.
(HCM 2000)
•Unlike saturation flow, capacity considers traffic signal
conditions
The formula for calculating capacity (c) is,
c = (g/C) · s · N
Where:
c = capacity (pcu/hour)
g = Effective green time for the phase in question (sec)
C = Cycle length (sec)
N = no. of lanes
s = Saturation flow rate (pcu/hour)
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Phase Design Steps
• Determination of cycle length (time)
• If tLi is the start-up lost time for a phase i, then the
total start-up lost time per cycle,
• where N is the number of phases.
• If start-up lost time is same for all phases, then the
total start-up lost time for cycle, L = N tL.
• If C is the cycle length in seconds, then the number
of cycles per hour = 3600/C.
• The total lost time per hour = 3600L/C.
• Substituting in L = N tL, then total lost time per hour
will be as follows:
• L =


N
i LtL 1
C
tN L..3600

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• The total effective green time Tg equal one hour
minus the total lost time in an hour as follows:
• Tg=
• Critical lane volume that can be accommodated
per hour is given by Vc = Tg/h
• Vc=
• Then, C= i
c
L
s
V
tN
1
.
Green splitting
• Total effective green time, Tg
• Actual green time , Gi

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• Example:
• The phase diagram with flow values of an
intersection with two phases is shown in the
following figure. The lost time and yellow time for
the first phase is 2.5 and 3 seconds,
respectively. For the second phase the lost time
and yellow time are 3.5 and 4 seconds,
respectively. If the cycle time is 120 seconds,
find the green time allocated for the two phases.
• Answer:
• Critical lane volume for the first phase, Vc1 = 1000
veh/hr.
• For the second phase, Vc2 = 600 veh/hr.
• The sum of the critical lane volumes = 1000+600 =
1600 veh/hr.
• Effective green time can be computed from equation
as
• Tg =120-(2.5-3.5)= 114 seconds.
• Green time for the first phase, g1 and second phase
can be computed from:
• ondsg sec25.71114
1600
1000
1 
ondsg sec75.42114
1600
600
2 

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• Actual green time can be determined from:
• First phase, G1 = 71.25-3+2.5 = 70.75 seconds.
• Second phase, G2 = 42.75-4+3.5 = 42.25
seconds.
• The phase diagram can be drawn in the
following figure.
Right Turn on Red
• Drivers in all 50 states are allowed to complete
a right turn on red but drivers must
come to a complete stop, yield to any and all
traffic and make sure there is no sign
prohibiting the turn, before completing a right
on red.

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Left Turn on Red?
• There is no left turn on red.
Multi-use Traffic Lanes
• In larger cities, the use of reversible lanes
increases the capacity of the existing streets.
• Center lanes are reversed to allow heavy
traffic, in one direction or the other, to have
more lanes.
• These lanes are marked with a green arrow or
a red X above the lane.

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10-Intersection Control ( Transportation and Traffic Engineering Dr. Sheriff El-Badawy )

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10-Intersection Control ( Transportation and Traffic Engineering Dr. Sheriff El-Badawy )