The document discusses traffic signals, which are devices controlling traffic flow at intersections using red and green lights for safe vehicle and pedestrian movement. It details their purpose, advantages, disadvantages, and components, including controllers and detectors that adjust signal timing based on real-time traffic data. Different types of signal operations are explained, including pre-timed, semi-actuated, and fully actuated systems based on vehicle detection and traffic volume.

1. DEPARTMENT OF CIVIL ENGINEERING
FACULTY OF ENGINEERING AND TECHNOLOGY
TRAFFIC SIGNALS
MUHAMMAD YASEEN 32-FET/BSCE/F14
MUHAMMAD JUNAID 35-FET/BSCE/F14

2. TRAFFIC SIGNALS:
Traffic signals are controlled devices which could alternatively
direct the traffic to stop and proceed at intersection using red
and green traffic light signals automatically.

3. Purpose of Traffic Signals
Traffic signals manage the right of way at signalized intersections to
provide for the safe and efficient movement of vehicles and pedestrians.
Traffic engineers and technicians develop and implement signal timing
at each intersection to distribute green time amongst the competing
traffic flows to provide for efficient operations.

4. NEED OF TRAFFIC SIGNALS
•Orderly flow of traffic.
•An opportunity for pedestrians or
vehicles to cross an intersection.
•Help reduce the number of conflicts.
•Reduce the frequency of accidents.
•Improve safety.

5. Signal Aspects
GREEN
AMBER
RED
The indication given by a signal is known as the signal aspect.

7. Traffic Signals : Advantages
• Provisions for side-street vehicles to enter the traffic stream.
• Provisions for the progressive flow of traffic in a signal-system corridor.
•Provisions for pedestrians to cross the street safely.
•Potential reduction of accidents, conflicts ensuring safety.

8. Traffic Signals : Disadvantages
• Excessive delay;
• Increased traffic congestion, air pollution and gasoline consumption;
•Disobedience of signals;
•Increased frequency of crashes, especially rear-end collisions.

9. Parts of a Traffic Signal
• Traffic signals have four main parts:
Display Controller
Detector Support

10. Signal display
The signal display is what the driver sees. A simple signal display
consists of three colors: red, yellow, and green.
• A typical signal display is more than 3 feet tall and weighs up to 50
pounds.

11. Signal Controller
The traffic signal controller is the “brain” at an intersection that tells each
signal display when to change colors. Years ago, traffic signals were
controlled by a simple electric mechanism that made the display change every
so many seconds, like a clock. These simple mechanisms were not able to
adjust when traffic changed during the day.
Later in the pre-computer era, electromechanical controllers were developed
that could be adjusted for the time of day. These controllers were much like
the switch timers in the local hardware store that have green and red pins to
set lights to go on and off on a predetermined schedule.

12. CONTINUE…………
Now, computerized traffic signal controllers get real-time information
about the presence of vehicles from sensors in the roadway and on
poles. Controllers adjust the amount of green time for different
movements based on sensor information. The most sophisticated
controllers and software programs allow for the coordination of signals
along a roadway, so that vehicles can travel through a succession of
intersections without having to stop.

14. DETECTORS
Detectors are used to identify the presence of a vehicle, so that the controller knows
how to adjust the amount of green time to provide. There are many types of
detectors. One type is known as the loop detector. The square black lines you may
see in the roadway as you approach an intersection are the visible part of the loop
detector, which is a thin wire buried in the roadway. When a vehicle drives over the
loop, it sends a message to the signal controller. The signal controller's software
evaluates the messages from all the loops at the intersection and changes the signal
timing appropriately. Small TV cameras can also be used to detect vehicles.

16. DETECTORS

17. Types of Signal Operation
Traffic signals can operate on a pretimed basis or may be partially or
fully actuated by arriving vehicles sensed by detectors. In networks, or
on arterials, signals may be coordinated through computer control.
TYPE1
PRE-TIMED
TYPE2
SEMI-
ACTUATED
TYPE3
FULLY
ACTUATED

18. Types of Signal Operation

19. PRE TIMED OPERATION
 A signal whose timing(cycle length,green time etc) is fixed over
specified time period and does not change in response to changes in
traffic flow at the intersection.
No vehicle detection is necessary at this mode of operation.

20. Pretimed Operation:
In pretimed operation, the cycle length, phase sequence, and timing of
each interval are constant. Each cycle of the signal follows the same
predetermined plan. “Multi-dial” controllers will allow different
pretimed settings to be established. An internal clock is used to activate
the appropriate timing. in such cases, it is typical to have at least an AM
peak, a PM peak, and an off-peak signal timing.

21. SEMI-ACTUATED OPERATION
 A signal whose timing(cycle length ,green time etc) is affected when
vehicle are detected(by video,inductance loop detecters,embeded-
pavement etc) on some but not all approaches is called semi-
actuated signal.
This mode of operation is found where a low volume road intersect a
high volume road.

22. Semi-actuated Operation
In semi-actuated operation, detectors are placed on the minor approach(es)
to the intersection; there are no detectors on the major street. The light is
green for the major street at all times except when a “call” or actuation is
noted on one of the minor approaches. Then, subject to limitations such as a
minimum major-street green, the green is transferred to the minor street.

23. CONTINUE………
The green returns to the major street when the maximum minor
street green is reached or when the detector senses that there is no
further demand on the minor street. Semi-actuated operation is often
used where the primary reason for signalization is ‘‘interruption of
continuous traffic,”

24. Fully Actuated
• A signal whose timing(cycle length,green time etc) is completely
influenced by the traffic volumes,when detected,on all of the
approaches.
Fully actuated signals are most commonly used at intersections of
two major streets where substantial variation exist in all approach
traffic volumes over the course of a day.

25. Full Actuated Operation
In full actuated operation, every lane of every approach must be
monitored by a detector. Green time is allocated in accordance with
information from detectors and programmed “rules” established in the
controller for capturing and retaining the green. In full actuated
operation, the cycle length, sequence of phases, and green time split
may vary from cycle to cycle.

26. SPACING BETWEEN TRAFFIC SIGNALS
REFERENCE;
http://www.ctre.iastate.edu/research/access/toolkit/4.pdf

27. DIMENSIONS
Reference
http://www.oksolar.com/images/signal_dimensions_large.jpg

28. HEIGHT
Reference;
http://lincoln.ne.gov/city/pworks/engine/dconst/gpp/gppdisc/sigshop/images/height.gif

29. Pedestrian Signals
Reference;
http://ichef1.bbci.co.uk/news/660/media/images/82931000/jpg/_82931048_trafficlights_
reuters.jpg

30. CONTINUE………….

31. BEACONS
• Beacons are generally used to identify a hazard or call attention to a
critical control device, such as a speed and continuously in accordance
with the programmed signal –timing.

32. Lane Use Control Signals
Reference
http://safety.fhwa.dot.gov/older_users/handbook/images/fig_24lg.jpg

33. REFERENCES:
TRAFFIC ENGINEERING BY WILLIAM R. MCSHANE
http://safety.fhwa.dot.gov/older_users/handbook/images/fig_24lg.jpg
http://ichef1.bbci.co.uk/news/660/media/images/82931000/jpg/_82931048_trafficlights_reuters.jpg
http://www.ctre.iastate.edu/research/access/toolkit/4.pdf

34. THE END
END
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