This document summarizes traffic light systems and coordination mechanisms. It discusses the basic components and functions of traffic lights including types of signals, sounds used to assist blind pedestrians, and priority systems for emergency vehicles. It also covers dedicated left turn signals and rules for turning at red lights that vary between jurisdictions. The conclusion discusses how intelligent traffic signal controllers can help improve traffic flow in cities.

1. Review on the topic traffic light
Kaushal kumar gupta*
*,* UG Stdents, Dr.M.G.R University
Abstract Introduction
A common mechanism that allows control of Traffic lights, which may also be known
vehicular flow in big cities is the use of traffic as stoplights, traffic lamps, traffic signals, signal
lights. Generally, each traffic light on an lights, robots or semaphores, are signalling
intersection is assigned a constant green time. devices positioned at road
In last years several agent-based traffic simu intersections, pedestrian crossings and other
lators have been proposed to show how better locations to control competing flows of traffic.
results can be achieved with respect to traffic Traffic lights were first installed in 1868
flow variables, like vehi cles’ route time and in London, United Kingdom, and are today used in
vehicles’ waiting time. It is possible to propose almost every city of the world. Traffic lights
agent-based coordination schemes where the alternate the right of way accorded to road users
green time of the traffic lights is assigned based by displaying lights of a standard color (red,
on the present conditions of traffic. Due to yellow/amber, and green) following a
those intelligent assignations on the traffic universal color code (and a precise sequence to
lights’ green time, it’s reasonable to think that enable comprehension by those who are color
vehicles’ waiting time could be reduced. In this blind).
paper we compare two traffic light coordina
tion mechanisms of an intersection that assign
Types
traffic lights’ green time based on approximate Single aspects
information about traffic conditions. It is
The simplest traffic light comprises either a
compared the vehicles’ waiting time on the
single or a pair of colored aspects that warns
traditional mechanism with respect to an
any user of the shared right of way of a possible
auction mech anism, in which the traffic lights
conflict or danger.Flashing Red: Treat as a stop
are “selfish”, and to a negotiation mechanism
sign. Also can signal the road is closed.
where the traffic lights work with a “non-
selfish” approach in the intersection. Our Flashing Yellow: Caution, crossing or road
results show that the negotiation mechanism, hazard ahead Flashing Green: Varies among
under certain con ditions, gets better results jurisdiction; can give permission to go straight
over the traditional and auction mechanisms. as well as make a left turn in front of opposing
traffic (which is held by a steady red light), or

2. can indicate the end of a green cycle before the red (beep ..... beep ..... beep) and a continuous
light changes to a solid yellow. buzzing sound when the lights are green.
In New South Wales, Victoria and Western
Dual aspects Australia the sound is produced in the same
These are often seen at railway crossings and at unit as the push buttons. This system
intersections of streets and emergency of assistive technology is also widely used at
department driveways. They will flash yellow busy intersections in Canadian cities.
when cross traffic is not expected, and turn red
to stop traffic when cross traffic occurs. The United Kingdom, the Puffin crossings and
their predecessor, the Pelican crossing, will
Three or more aspects make a slow beeping sound to indicate that it is
The standard is the red light above the green, safe to cross the road. The beeping sound is
with yellow between. When sideways, the disabled during the night time so as not to
arrangement depends on the rule of the road. disturb any nearby residents.
In right-lane countries, the green light is on the
right, and in left-lane countries, the left. Light for Public transport
Other signals are sometimes added for more Traffic lights for public transport often use
control, such as for public transportation and signals that are distinct from those for private
permissive turns. For a brief time, they also turn traffic. They can be letters, arrows or bars of
red in all directions, to clear any traffic in the white or colored light.
intersection. The delay can depend on traffic,
road conditions, and the kind of intersection. In Portland, Oregon, the tram signals feature an
orange horizontal bar and a white vertical bar.
The three-aspect standard is also used at locks Some systems use the letter B for buses, and T
on the Upper Mississippi River. Red means that for trams.
another vessel is passing through. Yellow means
that the lock chamber is being emptied or filled In Russia, dedicated traffic signals for public
to match the level of the approaching vessel. transport (tram, trolleybus or bus) have four
After the gate opens, green means that the white lights that form the letter T. If the three
vessel may enter. top lamps are lit, this means "stop". If the
bottom lamp and some lamps on the top row
In Quebec, lights are often sideways, but each a are lit, this means permission to go in a
different shape: red is a square (larger than the direction shown. In case of a tram signal, if
normal circle), yellow is a diamond, and green is there are no tram junctions on an intersection,
a circle. a simpler system of one yellow signal in the
form of letter T is used instead; the tram must
Sounds proceed only when the signal is lit.
In some jurisdictions such as Australia, In North European countries the tram signals
pedestrian lights are associated with a sound feature white lights of different forms: "S" for
device, for the benefit of blind and visually "stop", "—" for "caution" and arrows to permit
impaired pedestrians. These make a slow passage in a given direction.
beeping sound when the pedestrian lights are

3. been passed by the vehicle that triggered the
preemption.
In lieu of pre-emptive mechanisms, in most
jurisdictions, emergency vehicles are not
required to respect traffic lights, but must
activate their own emergency lights when
crossing an intersection against the light, in
order to alert oncoming drivers to the
preemption.
Preemption
Turning signals and rules
Some regions have signals that are
interruptible, giving priority to special traffic.
Such traffic light preemption is usually reserved
foremergency vehicles such as fire
apparatus, ambulances, and police squad cars,
though sometimes mass transit vehicles
includingbuses and light rail trains can interrupt
lights. Most of the systems operate with small
transmitters that send radio
waves, infraredsignals, or strobe light signals that
are received by a sensor on or near the traffic
lights. Some systems use audio detection,
where a certain type of siren must be used and
detected by a receiver on the traffic light
structure.
Upon activation the normal traffic light cycle is
suspended and replaced by the "preemption
sequence": the traffic lights to all approaches to
the intersection are switched to "red" with the
exception of the light for the vehicle that has
triggered the preemption sequence. .
Sometimes, an additional signal light is placed
In some instances, traffic may turn left (in left-
nearby to indicate to the preempting vehicle
driving jurisdictions) or right (in right-driving
that the preempting sequence has been
jurisdictions) after stopping at a red light,
activated and to warn other motorists of the
providing they give way to the pedestrians and
approach of an emergency vehicle. The normal
other vehicles. In some places that generally
traffic light cycle resumes after the sensor has
disallow this, a sign next to the traffic light
indicates that it is allowed at a particular

4. intersection. Conversely, jurisdictions that left turn signals, a left-pointing arrow turns
generally allow this might forbid it at a green when traffic may turn left without
particular intersection with a "no turn on red" opposing traffic and pedestrian conflict, and
sign, or put a green arrow to indicate turns red or disappears otherwise. Such a signal
specifically when a turn is allowed without is referred to as a "protected" signal if it has its
having to yield to pedestrians (this is usually own red phase; a "permissive" signal does not
when traffic from the perpendicular street is have such a feature. Three standard versions of
making a turn onto one's street and thus no the permissive signal exist: One version is a
pedestrians are allowed in the intersection horizontal bar with five lights - the green and
anyway). Some jurisdictions allow turning on yellow arrows are located between the
red in the opposite direction (left in right- standard green and yellow lights. A vertical 5-
driving countries; right in left-driving countries) light bar holds the arrows underneath the
from a one-way road onto another one-way standard green light (in this arrangement, the
road; some of these even allow these turns yellow arrow is sometimes omitted, leaving only
from a two-way road onto a one-way the green arrow below the solid green light, or
road.[22] Also differing is whether a red arrow possibly an LED based device capable of
prohibits turns; some jurisdictions require a "no showing both green and yellow arrows within a
turn on red" sign in these cases. A study in single lamp housing). Some newer LED turn
the State of Illinois (a right-driving jurisdiction) arrows seen in parts of Canada are capable of
concluded that allowing drivers to proceed multicolored animation. Such lights will often
straight on red after stopping, at specially display a flashing and animated green or yellow
posted T-intersections where the intersecting arrow when the dedicated turn is allowed, but
road went left only, was dangerous.[citation then transform into a red arrow on a white
needed]
Proceeding straight on red at T- background with a red line through it,
intersections where the intersecting road went emphasising that the turn is no longer allowed.
left only used to be legal in Mainland China, These lights will also often have the words "NO
with right-hand traffic provided that such TURN" displayed, or an explanatory reason why
movement would not interfere with other the turn is not allowed, such as "TRAIN" in the
traffic, but when the Road Traffic Safety Law of case of a rail or light rail crossing. A third type is
the People's Republic of China took effect on 1 known as a "doghouse" or "cluster head" - a
May 2004, such movement was outlawed.[23] In vertical column with the two normal lights is on
some other countries, the permission is the right side of the signal, a vertical column
indicated by a flashing yellow arrow (cars do with the two arrows is located on the left, and
not have to stop but must give way to other the normal red signal is in the middle above the
cars and pedestrians). two columns. Cluster signals
in Australia and New Zealand use six signals, the
Another distinction is between intersections sixth being a red arrow that can operate
that have dedicated signals for turning across separately from the standard red light. In a
the flow of opposing traffic and those that do fourth type, sometimes seen at intersections
not. Such signals are called dedicated left-turn in Ontario and Quebec, Canada, there is no
lights in the United States and Canada (since dedicated left-turn lamp per se. Instead, the
opposing traffic is on the left). With dedicated normal green lamp flashes rapidly, indicating

5. permission to go straight as well as make a left opposing traffic to clear, attempting to make an
turn in front of opposing traffic, which is being illegal left turn on red. A dedicated left-turn
held by a steady red lamp. (This "advance signal that appears at the end of the green
green," or flashing green can be somewhat phase is called a lagging turn. If there is no left-
startling and confusing to drivers not familiar turn signal, the law requires one to yield to
with this system. This also can cause confusion oncoming traffic and turn when the intersection
amongst visitors to British Columbia, where a is clear and it is safe to do so. Nevertheless, it is
flashing green signal denotes a pedestrian increasingly and disturbingly common in at least
controlled crosswalk. Another interesting the U.S. to see drivers who do not yield in the
practice seen at least in Ontario is that cars absence of a dedicated signal, cutting off traffic
wishing to turn left that arrived after the left that has right-of-way and is starting to head
turn signal ended can do so during the yellow across the intersection. In the U.S., many older
phase, as long as there is enough time to make inner-city and rural areas do not have dedicated
a safe turn. left-turn lights, while most newer suburban
areas have them. Such lights tend to decrease
A flashing yellow arrow, which allows drivers to the overall efficiency of the intersection as it
make left turns after giving way to oncoming becomes congested, although it makes
traffic, is becoming more widespread in the intersections safer by reducing the risk of head-
United States, particularly in Oregon. In the on collisions and may even speed up through
normal sequence, a protected green left-turn traffic, but if a significant amount of traffic is
arrow will first change to a solid yellow arrow to turning, a dedicated turn signal helps eliminate
indicate the end of the protected phase, then to congestion.
a flashing yellow arrow, which remains flashing
until the standard green light changes to yellow Conclusion
and red. These generally take the form of four
signal sections (green, yellow, yellow arrow, The improvement of town traffic condition is
red). On some newer signals, notably in the city largely dependent on the modern ways of
of Bend, the green and flashing yellow arrows traffic management and control. Advanced
emanate from the same light section through traffic signal controllers and control system
the use of a dual-color LED array, while the solid contribute to the improvement of the urban
yellow arrow is mounted above it. traffic problem. The intelligent of traffic signal
controller that is introduced in this project with
Generally, a dedicated left-turn signal is powerful functions and hardware interface.
illuminated at the beginning of the green phase Good quality social benefit has been made
of the green-yellow-red-green cycle. This is through the application of the intelligent traffic
called a leading turn. This allows left-turn controller in practice, and the application result
traffic, which often consists of just a few cars, to shows that the intelligent traffic signal
vacate the intersection quickly before giving controller will improve.
priority to vehicles traveling straight. This
increases the throughput of left-turn traffic
while reducing the number of drivers, perhaps
frustrated by long waits in heavy traffic for