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This work was initiated, designed and constructed by uche iyk. For more information contact iyk with this number 08034117423. E-mail: [email protected] . © Nwoke U. Iyk 2010. All rights reserved. No reproduction, copy or transmission in any form whatsoever of this work or part thereof may be made without prior permission of the author.
uc-iyk®
2010
uche iyk
uc-iyk
2/15/2010
DESIGN, CONSTRUCTION AND TESTING OF HARDWARE IMPLEMENTATION OF INTELLIGENCE
TRAFFIC LIGHT CONTROL CIRCUIT
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Life has taught me that future gold or success is already delivered into the hand of
every creature, man determines how to achieve it.
Iyk, 2003.
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Pierre Vivant’s famous “Traffic Light Tree” near Canary Wharf, London
The Traffic Light tree was created by French sculptor Pierre Vivant (1952- ) following a competition run by the Public Art Commissions Agency. It is situated on a roundabout near Canary Wharf, at the junctions of Heron Quay Bank, Marsh Wall and Westferry Road. In one of London’s financial districts.
Eight metres tall and containing 75 sets of lights, each controlled by computer, Vivant described the project thus:
“The sculpture imitates the natural landscape of the adjacent London Plane Trees, while the changing pattern of the pattern of the lights reveals and reflects the never ending rhythm of the surrounding domestic, financial and commercial activities.”
The Public Art Commission Agency were quick to point out that:
“The arbitrary cycle of light changes is not supposed to mimic the seasonal rhythm of nature, but the restlessness Canary Whary.
The Traffic Light tree was installed in 1998 on the site of a plane tree, that was choking to death as a result of pollution. It was initially hoped that the lights would be triggered to show flurries of activity on the London Stock Exchange, but this proved to be too expensive to put into practice.
Although some motorists were initially confused by the traffic lights, mistaking them for real signals, the folly soon become a favourite among both tourists and locals.
In 2005, Saga Motor Insurance commissioned a survey asking British motorists about the best and worst roundabouts in the country. The Traffic Light tree was the clear favourite.
uc-iyk. 2010.
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DESIGN, CONSTRUCTION AND TESTING OF
HARDWARE IMPLEMENTATION OF INTELLIGENCE
TRAFFIC LIGHT CONTROL CIRCUIT
FEBRUARY, 2010.
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DEDICATION
This work is dedicated most especially, to the Almighty God for His
benevolence on us towards the completion of this work. I gratefully
dedicate it to my parents, to children of the world and to all lovers of
electronics.
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TABLE OF CONTENT
Title page …………………………………………………………………...i
Dedication ………………………………………………………………....iii
Table of contents ……………………………………………….…………v
Abstract ………………………………………………............................vii
List of figures ...…………………………………………………..………viii
List of tables …………………………………………………….………..ix
CHAPTER ONE
1.0 Introduction................................................................................1
1.1 The meaning of traffic light........................................................1
1.2 Traffic police and early signals..................................................2
1.3 A brief history of traffic signals...................................................3
1.4 Review of traffic light systems...................................................4
1.5 The basics of traffic lights..........................................................5
1.6 Uses of traffic signals................................................................6
1.7 General description and the importance of traffic light............11
1.8 Types of traffic lights, turning signals and rules......................12
CHAPTER TWO
2.0 Literature review....................................................................20
2.1 Overview of some of the previous traffic light projects.................21
2.2 Operations of traffic light controller and its benefits..............27
2.3 State machine design............................................................29
2.3.1 Notion of states in sequential machines................................30
2.4 Traffic signal timing................................................................32
2.4.1 Planned special events, incident, & emergency management......32
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2.5 The intelligent of the traffic light controller...................................35
2.5.1 Possible directions of the traffic light controller............................37
2.6 Important component of the traffic light controller........................38
2.6.1 Display unit of the traffic light controller.......................................38
2.6.2 ICs in the traffic light controller circuit..........................................39
CHAPTER THREE
3.0 Circuit design.........................................................................42
3.1 Design considerations............................................................42
3.2 Timing circuit..........................................................................43
3.3 The 80 output sequencing circuit...........................................45
3.3.1 Manual control circuits...........................................................47
3.4 Signal control circuit and 80 step led drive circuit…………...47
3.5 Circuit design for emergency, VIPs, pedestrian crossing
etcetera……………………………………………………………53
3.6 Power supply for the traffic light……………………………….55
CHAPTER FOUR
4.0 Construction and testing........................................................57
4.1 Construction details...............................................................57
4.2 Testing...................................................................................59
4.3 Construction precautions.......................................................59
CHAPTER FIVE
5.0 Conclusion.............................................................................63
5.1 Summary of work done..........................................................63
5.2 Recommendations..................................................................64
Reference.........................................................................................66
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ABSTRACT
Vehicular travel is increasing throughout the world, particularly in
large urban areas. Therefore the need arises for simulating and optimizing
traffic control algorithms to better accommodate this increasing demand.
Automated Traffic light control is playing more and more important roles in
modern management and controls of urban traffic to reduce the accident
and traffic jam in road. The traffic light controller is a sequential machine to
be analyzed and programmed through a multi step process. The device
that involves an analysis of existing sequential machines in traffic lights
controllers, timing and synchronization and introduction of operation and
flashing light synthesis sequence. This project operates red, yellow (amber)
and green lights in the correct sequence for a junction traffic light. The time
taken for the complete red - red & yellow - green - yellow sequence can be
varied with the timing circuit.
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LIST FIGURES
Figure 2.1: Block Diagram of Mealy’s Finite State Machine.............31
Figure 2.2: Block Diagram of Moore’s Finite State Machine............31
Figure 2.3: Flow of traffic in all possible directions...........................37
Figure 3.1: 80 Output Sequencing Circuit and traffic light drive circuit
..........................................................................................................44
Figure 3.2: Signal control circuit........................................................49
Figure 3.3: Traffic lights display circuit..............................................50
Figure 3.4: Flow of traffic in all possible directions…………………..51
Figure 3.5: Emergency, pedestrian, VIPs circuit for the traffic light...54
Figure 3.6: power supply for the traffic light…………………………..65
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LIST OF TABLE
Table 3.1: Simultaneous states of signals for all the traffic.............52
Table 3.2: Boolean functions for all the signal conditions………….53
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CHAPTER ONE
1.0 INTRODUCTION
1.1 THE MEANING OF TRAFFIC LIGHT
A traffic light is a collection of two or more coloured lights found at
some junctions and pedestrian crossings which indicates whether it is safe
and/or legal to continue across the path of other road users. In Nigeria,
traffic lights are widely used both on major roads and in built-up areas.
Their numbers have increased exponentially since they were first invented
in 1868 [1].
Traffic lights, also known as traffic signals, stop lights, traffic lamps,
stop-and-go lights, robots or semaphore, are signalling devices positioned
at road intersections, pedestrian crossings, and other locations to control
competing flows of traffic. Traffic lights have been installed in most cities
around the world to control the flow of traffic. They assign the right of way
to road users by the use of lights in standard colours (Red - Amber -
Green), using a universal colour code (and a precise sequence, for those
who are colour blind). They are used at busy intersections to more evenly
apportion delay to the various users. The most common traffic lights consist
of a set of three lights: red, yellow (officially amber), and green. When
illuminated, the red light indicates for vehicles facing the light to stop; the
amber indicates caution, either because lights are about to turn green or
because lights are about to turn red; and the green light to proceed, if it is
safe to do so.
There are many variations in the use and legislation of traffic lights,
depending on the customs of a country and the special needs of a
particular intersection. There may, for example, be special lights for
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pedestrians, bicycles, buses, trams, etc; light sequences may differ; and
there may be special rules, or sets of lights, for traffic turning in a particular
direction. Complex intersections may use any combination of these. Traffic
light technology is constantly evolving with the aims of improving reliability,
visibility, and efficiency of traffic flow.
1.2 TRAFFIC POLICE AND EARLY SIGNALS
Traffic police officers operated semaphores and early traffic lights by
hand. City officials didn't think drivers would obey the signals otherwise.
The traffic officers judged the traffic and decided when to change the
signal. To alert traffic that the signal was about to change, they blew a
whistle. Besides cars and trucks, traffic included street cars (vehicles
travelling on rails) and horse-drawn vehicles. With all this traffic, one
problem that officers had was being able to see and be seen by drivers,
especially at congested intersections.
To give traffic officers a wider view, many cities in the United States
started using traffic towers in the late 1910s and 1920s. These towers were
small booths several feet above street level on street corners or on
concrete islands in the middle of a street or intersection. The officers inside
the towers operated coloured lights or semaphores or waved their arms.
Detroit was a hotbed of innovation for traffic signals. In 1917, Detroit
installed the first traffic tower in the United States at the intersection of
Woodward Avenue and Michigan Avenue [2]. In 1920, Detroit became the
first city to use red, green, and yellow lights to control traffic. And a Detroit
police officer named William L. Potts invented the 4-way, 3-color traffic
signal. During the 1920s inventors came up with plenty of different designs
for traffic signals. One thing these signals usually had in common was that
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someone had to push a button or flip a switch to change the signal.
Imagine the thousands of police officers whose job it was to operate signals
and enforce traffic laws at intersections. Once automated signals were
invented, traffic officers were freed up for other duties.
1.3 A BRIEF HISTORY OF TRAFFIC SIGNALS
The first traffic lights actually had their roots in the railway signals used
at the time, where two gas lamps, one red and one green, would be
alternately hidden by a semaphore arm depending on whether the arm was
in a horizontal position or at a 30° angle. The fir st lights were installed
outside the Houses of Parliament in London on 10 December, 1868 to
control the increasing number of vehicles there. However, according to
some sources, they later exploded and injured the policeman operating
them.
The first electric lights were developed in the USA in the early 20th
Century. Various people lay claim to the invention of the modern traffic light
[3]. These include:
• Lester Wire, a Salt Lake City policeman who set up the first red-green
electric traffic lights in 1912.
• James Hoge, from Cleveland, who in 1914 designed some red-green
electric lights with a buzzer which sounded when the lights changed.
• William Potts from Detroit, who designed the first three-colour electric
traffic lights in 1920.
• John Harriss, a Police Commissioner from New York who developed
the first interconnected three-colour electric traffic lights in 1922.
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• Garrett Morgan, from Cleveland, who in 1923 designed a cross-
shaped signalling device which is often mistakenly referred to as the
first traffic light.
Once the USA had finished reinventing the traffic light, it was adopted
in the UK. The first automatic lights were installed in Princes Square in
Wolverhampton. Nowadays, traffic lights are often operated by complex
computer software designed to optimise traffic flow.
1.4 REVIEW OF TRAFFIC LIGHT SYSTEMS
A traffic light system is an electronic device that assigns right of way
at an intersection or crossing or street crossing by means of displaying the
standard red, yellow and green coloured indications. In addition, it also
works in conjunction with pedestrian displays to assign pedestrian crossing
right of way. A traffic light, also known as traffic signal, stop light, stop-and-
go lights, is a signalling device positioned at a road intersection, pedestrian
crossing, or other location in order to indicate when it is safe to drive, ride,
or walk using a universal colour code (and a precise sequence, for that are
colours blind).
Traffic light optimization is a complex problem. Even for T-junction
there might be no obvious optimal solution. With crossroad junction, the
problem becomes even more complex, as the state of one light influences
the flow of traffic towards many other lights. Another complication is the fact
that flow of traffic constantly changes, depending on the time of day, the
day of the week, and the time of year. Roadwork and accidents further
influence complexity and performance.
Nowadays, a red light meant traffic in all directions had to stop. A
yellow light meant cross-town traffic would have to slow and a green light
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would to go or proceed. The development of an intelligent control structure
ensures an optimal solution for all participants in the transportation and
road traffic system.
There are different ways controlling road intersections. In the simplest
cases the right-hand rule or, if the traffic is higher, a roundabout or the
signal of a policeman can help steer the traffic. However, especially in big
cities, in the complicated cases when the roads in the intersection have
several lanes, the use of traffic lights cannot be avoided. An additional
issue arises when in the intersection not only roads but also railroad tracks
take part, what often occurs in suburban traffic situations. The most
common way to handle this type of intersection is the conventional cyclic
lights control. In more enhanced control, the traffic in different directions is
monitored by sensors and the signals thus obtained control the traffic lights.
In this method the control is adapting to the traffic.
1.5 THE BASICS OF TRAFFIC LIGHTS
The most basic traffic light consists of three bulbs with different
coloured lenses, which from top to bottom are red, amber and green. In
Nigeria, the lights commonly use a sequence of four phases:
1. Red— this indicates that traffic must stop behind the line. It is
compulsory for all road users to do so. Some traffic lights even have
cameras to catch drivers breaking this law.
2. Red and Amber— this combination of bulbs indicates that the lights
are about to change to green, and gives drivers time to release their
handbrake and prepare to drive off as soon as they are allowed to do
so. This phase was first introduced in 1958.
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3. Green— this indicates that traffic may pass through the junction,
provided that it is safe to do so and the way is clear. Some junctions
are marked with a hash of yellow lines forming a box, which indicates
that drivers must not stop on the box unless they are turning right and
their exit is clear.
4. Amber— this warns traffic that it should stop unless it is unsafe to do
so. In the UK and Nigeria it is legal to pass through an amber light, as
the phase exists to warn drivers not yet at the junction that they will
have to stop.
Traffic lights at junctions will always follow this pattern, with conflicting flows
of traffic being forced to take turns. Often the green bulb is replaced with
two or more green arrows or filter lights, which indicate that traffic turning
left or right may go, while a red light remains to instruct oncoming traffic to
wait. It is now quite common for vehicles turning right to have to wait for a
separate filter light, even if the way is clear. Despite being relatively simple,
filter arrows are often 'mistaken' for an instruction to go by drivers who want
to turn a different way to that shown. Problems are also known to arise
from motorists watching the other lights at junctions and anticipating their
own movement, and so shades are used to hide the lights from both drivers
and from the sun, which would reduce their visibility. It is interesting to note
that the UK is one of only a few countries not to have a 'left on red' rule,
where cars are allowed to pass through a red light if it is safe to turn left; in
the UK, red lights and filter lights must always be obeyed [4].
A recent improvement in traffic light technology has come with the
development of red, amber and green light-emitting diodes (LEDs). Arrays
of these tiny bulbs can be used to replace the existing light bulbs in traffic
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lights and are clearer and more energy-efficient. It is estimated that
replacing all the traffic light bulbs in Nigeria with LEDs would save enough
energy and money.
1.6 USES OF TRAFFIC SIGNALS
• PEDESTRIAN CROSSINGS
Many junctions also have pedestrian crossings built into them, where
red and green signals in the shape of a walking (green) or standing (red)
figure indicate to pedestrians whether it is safe to cross. There is also a
blank phase where both signals are unlit, indicating that it is still safe to
continue crossing but there is not enough time for the average 90-year-old
to make it in time if they start now. These crossings often have associated
push-buttons for use by pedestrians, but their only apparent action is to
display the word WAIT in large, friendly letters. Some of these boxes do,
however, have a small knob underneath which revolves when it is safe to
cross, which can be useful for the visually impaired. It is important to note
that Nigeria, although it is not illegal to jaywalk, doing so violates the
Highway Code and those responsible are liable for any resulting accident
[5]. Those using pedestrian crossings on side roads have right of way over
vehicles once they have begun to cross.
A different sequence to the one mentioned above is used at pelican
crossings, where the crossing is not associated with a junction, but is
designed purely to allow pedestrians to cross busy roads. The push buttons
at these crossings actually stop the traffic after a short delay, and the green
figure is often accompanied by a beeping sound. The red and amber phase
is replaced by a flashing one, indicating that drivers may continue if there
are no pedestrians on the crossing; at the same time the beeping stops and
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a flashing green figure indicates to pedestrians still waiting to step out onto
the crossing that they should wait for the next green man signal to give
them right of way. Pedestrians already on the crossing should simply
continue to the other side as normal.
Similar crossings are provided for cyclists (toucan crossings) and for
horse riders (Pegasus crossings). These crossings sometimes feature red
and green cycles or horses. Another development on the theme of the
pelican crossing is the puffin crossing, where a sensor detects if there are
pedestrians on the crossing, making the flashing phase used on pelican
crossings obsolete. These crossings do, however, cause confusion, as the
red and green men are sited above the push button and not on the
opposite side of the road. There are some crossings that do not involve any
coloured light sequences. The zebra crossing features a pair of flashing
amber Belisha Beacons, while badger crossings do not have any lights at
all.
OTHER USES
Although their main purpose is to control traffic at junctions and to allow
pedestrians to cross safely, traffic lights are used in a variety of situations,
including:
• Traffic control at road works, where a pair of three-bulb traffic lights
has replaced the manual STOP/GO signs.
• Lights at level crossings and drawbridges, where a single steady
amber light precedes a pair of flashing red lights indicating that traffic
must stop. These are also used to allow emergency services vehicles
out of depots on busy roads, and to allow animals to be herded
across main roads.
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• Lane control on motorways, where white arrows instruct drivers to
change lane or leave the motorway, while red crosses indicate closed
lanes.
• Lane control on busy roads where the middle lane is used by rush-
hour traffic heading one way in the morning and the other in the
afternoon. Here, green arrows indicate open lanes and red crosses
indicate closed ones.
• As a colour-based system of rating something completely
unconnected with driving, where red usually means 'bad' or
'unavailable' and green means 'good' or 'in plentiful supply'.
Applications can range from rating the severity of an emergency to
use at 'traffic light parties', where the colours give an indication of
one's availability to the proposition of a relationship.
• At the cheesy discos of the 1970s, where actual traffic lights were
used as disco lights, mostly ignoring the standard sequences.
• In traffic-light jelly.
Emergency vehicles are effectively exempt from this rule, but only when
their emergency lights and sirens are on to warn other road users to make
way. Although emergency vehicles have a duty of care to other road users,
other motorists are expected to give up their right of way to avoid
accidents. Although most drivers tend to avoid using the parking brake
while waiting at lights, despite this being part of the driving test criteria. Or
'right on red' in countries where cars drive on the right. Examples of
countries where this rule sometimes applies include the USA, France,
Belgium, Greece, Nigeria etc. This means to cross the road when the traffic
lights indicate that you should wait, and is illegal in the USA. This is the set
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of rules that should be adhered to when using roads and pavements in
Nigeria. Most of these are not actual laws, but are used to determine
liability in the case of an accident. These are lollipop-shaped signs with a
red STOP sign on one face and a green GO sign on the other, and are
rotated by a worker to indicate which queue of traffic is free to go.
At these parties, green or amber are used to indicate single status, with
amber indicating that the wearer is not necessarily looking for a new
relationship. Red is worn by those who are already taken or are just not
interested.
1.7 GENERAL DESCRIPTION AND THE IMPORTANCE OF TRAFFIC
LIGHT
The monitoring and control of city traffic is becoming a major problem
in many countries. With the ever increasing number of vehicles on the road,
the Traffic Monitoring Authority or the Transportation Ministry as the
authority is known here in Nigeria, has to find new ways or measures of
overcoming such a problem. The measures taken are development of new
roads and flyovers in the middle of the city; building of several rings such
as the inner ring road, middle ring road and outer ring road; introduction of
city buses such as the Lagos rapid transit (LRT) in Lagos, restricting of
large vehicles in the city during peak hours; and also development of
sophisticated traffic monitoring and control systems. In the city of Lagos,
the registration of new vehicles each year increased by about twenty per
cent. This increment is rather alarming and even with the development of
the LRT and new roads other measures have to be stepped up and
introduced as quickly as possible. In Abuja the problem of traffic flow during
peak hours has somewhat been under control by city traffic policemen. In
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last February the movement of traffic in the city was chaotic when traffic
policemen were taken off their duties of manning the junctions. It was learnt
that the Abuja municipal wanted to test their automatic traffic control
system that had recently been installed which was still in its initial stage [6].
It is understandable that automatic control systems should relieve humans
from manual control; however, such automatic system does not work well
in many circumstances especially during oversaturated or unusual load
conditions which could be due to limitations of the algorithms or sensing
devices. In this respect manual control seems to be better due to the
intelligence of the traffic policemen in understanding the traffic conditions at
the respective junctions.
Transportation research has the goal to optimize transportation flow of
people and goods. As the number of road users constantly increases, and
resources provided by current infrastructures are limited, intelligent control
of traffic will become a very important issue in the future. However, some
limitations to the usage of intelligent traffic control exist. Avoiding traffic
jams for example is thought to be beneficial to both environment and
economy, but improved traffic-flow may also lead to an increase in
demand.
Cars in urban traffic can experience long travel times due to inefficient
traffic light control. Optimal control of traffic lights using sophisticated
sensors and intelligent optimization algorithms might therefore be very
beneficial. Optimization of traffic light switching increases road capacity and
traffic flow, and can prevent traffic congestions. Traffic light control is a
complex optimization problem and several intelligent algorithms, such as
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fuzzy logic, evolutionary algorithms, and reinforcement learning have
already been used in attempts to solve it.
1.8 TYPES OF TRAFFIC LIGHTS, TURNING SIGNALS AND RULES
• Three-set lights
The universal standard is for the red to be above the green, and if there
is also an amber it is placed in the middle. If the three-set lights are
mounted horizontally, the red will typically be to the left of the green. The
standards apply whether the country drives on the left or the right, but the
placement of the mountings on the road would be mirror images of the
other.
Each country has differing road rules, including how traffic lights are to
be interpreted. For example, in some countries, a flashing yellow light
means that a motorist may proceed with care if the road is clear, giving way
to pedestrians and to other road vehicles that may have priority (essentially
the same as arriving at a non-signalized intersection and not facing a stop
sign). A flashing red may be treated as a regular stop sign. In most
countries, the sequence is green (go), amber (prepare to stop), and red
(stop). In New Zealand and Canada, amber officially means 'stop (unless it
would cause an accident to do so)' but in practice, is treated as 'prepare to
stop'. In some places, such as Nigeria, the sequence is red (stop), red and
amber (stop), green (go if clear), amber (stop). In Russia, Serbia, Austria,
Israel, and parts of Canada and Mexico, the green light flashes for a few
seconds before the amber light comes on. The single flashing amber signal
is used in the UK, Ireland and Australia at Pelican crossings. It is used in
Serbia and the United States to mark places where greater attention is
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needed (dangerous crossings, sharp curves etc.). In Canada, flashing
amber light means "drive with caution" and is frequently combined with a
flashing red light (meaning "stop") at four way intersections. In many S.E,
Asian countries (e.g. Thailand) a flashing amber light indicates a driver may
precede cautiously across a junction where signals only operate at busy
periods.
• Pedestrian crossing lights
Traffic lights for pedestrians normally have two main lights: a red light that
means 'stop' and a green light that means 'go' (or, more correctly, 'proceed
with caution'). There is usually a flashing phase (red in the US and
Australia, green in Europe) that means 'complete your crossing'. In most
locales in North America, the colours used are a red orange ("Portland
orange") for "stop/wait" and a bluish-white ("lunar") for "go." While the
"walk" signal is generally a walking human figure, North American
pedestrian signals usually show an upraised hand for "stop," while most
other countries display a standing human figure. Some older American
signals display the verbal commands "Walk" (lunar white or green) and
"Don't Walk" or "Wait" (red-orange).
At selected pedestrian crossings in some countries, pedestrian traffic
lights include a type of siren, beeper or warbler, which sounds in order to
alert visually impaired pedestrians that it is safe to cross. These may be set
to a timer and only sound at day time, to avoid annoying residents. Some
other intersections include a white strobe light mounted inside the red light
that flashes every few seconds when the light is red. This is mainly used
when a new traffic light is installed or where running a red light has proven
to be a problem. Some also include tactile warnings, like a vibrating plate,
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or a rotating cone, to help people with hearing impairment or visual
impairment cross the road and street. In Washington D.C, North America.
The pedestrian signal is accompanied with a countdown timer. This
indicates the allocated time allowed to cross. The numbers start off white
colour and at around 8-5 seconds turn red. They flash along with the white
flashing man and the red hand.
Some pedestrian crossing lights are only activated after a pedestrian
press an activating button, while others operate automatically and others
still operate automatically but only at certain times of the day. In some
jurisdictions, at intersections where there are no pedestrian crossing lights
in operation, the normal three-set lights also apply to pedestrians crossing
the street [7].
• Lights for public transport
Traffic lights for public transport often use signals that are distinct from
those for private traffic. They can be letters, arrows or bars of white or
coloured light. In some places the tram signals feature a horizontal white
bar and an orange vertical bar. Some systems use the letter B for buses,
and T for trams. There are also signs of a bicycle for cyclists.
• Colours
The most common colours used in traffic lights are red, amber (yellow),
and green. Red typically means stop or high level of danger; amber
typically means caution; and green typically means proceed with care.
Usually, the red light contains some orange in its hue, and the green light
contains some blue, to provide some support for people with red-green
colour blindness. In the UK, traffic lights typically have a white reflective
border which enables colour blind users, during the hours of darkness, to
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distinguish the lights from other similarly-coloured street or automobile
lights, and to allow them to distinguish the lights by vertical position.
TURNING SIGNALS AND RULES
4-state lights (Nigeria):
1. Stop
2. Stop
3. Go if clear
4. Stop
In some instances, traffic may turn left (in left-driving jurisdictions) or
right (in right-driving jurisdictions) after stopping at a red light, providing
they give way to the pedestrians and other vehicles. In some cases which
generally disallow this, a sign next to the traffic light indicates that it is
allowed at a particular intersection. Conversely, jurisdictions which
generally allow this might forbid it at a particular intersection with a "no turn
on red" sign, or might put a green arrow to indicate specifically when a turn
is allowed without having to yield to pedestrians (this is usually when traffic
from the perpendicular street is making a turn onto one's street and thus no
pedestrians are allowed in the intersection anyway). Some jurisdictions
allow turning on red in the opposite direction (left in right-driving countries;
right in left-driving countries) from a one-way road onto another one-way
road; some of these even allow these turns from a two-way road onto a
one-way road. Also differing is whether a red arrow prohibits turns; some
jurisdictions require a "no turn on red" sign in these cases.
A study in the State of Illinois (a right-driving jurisdiction) concluded
that allowing drivers to proceed straight on red after stopping, at specially
posted T-intersections where the intersecting road went only left, was
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dangerous. Proceeding straight on red at T-intersections where the
intersecting road went only left was once legal in Mainland China with right-
hand traffic provided that such movement would not interfere with other
traffic, but when the Road Traffic Safety Law of the People's Republic of
China took effect on 1 May 2004, such movement was outlawed. In some
other countries the permission is indicated by flashing amber arrow (cars
do not have to stop but must give way to other cars and pedestrians).
Another distinction is between intersections that have dedicated signals for
turning across the flow of opposing traffic and those that do not. Such
signals are called dedicated left turn lights in the United States and Canada
(since opposing traffic is on the left). With dedicated left turn signals, a left-
pointing arrow turns green when traffic may turn left without conflict, and
turns red or disappears otherwise. Such a signal is referred to as a
"protected" signal if it has its own red phase; a "permissive" signal does not
have such a feature. Three standard versions of the permissive signal
exist: One version is a horizontal bar with five lights - the green and yellow
arrows are located between the standard green and yellow lights. A vertical
5-light bar holds the arrows underneath the standard green light (in this
arrangement, the yellow arrow is sometimes omitted, leaving only the
green arrow below the solid green light, or possibly an LED based device
capable of showing both green and yellow arrows within a single lamp
housing). A third type is known as a "doghouse" or "cluster head" - a
vertical column with the two normal lights is on the right side of the signal, a
vertical column with the two arrows is located on the left, and the normal
red signal is in the middle above the two columns. Cluster signals in
Australia and New Zealand use six signals, the sixth being a red arrow
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which can operate separately from the standard red light. In a fourth type,
sometimes seen at intersections in Ontario and Quebec, Canada, there is
no dedicated left-turn lamp per se.
Instead, the normal green lamp flashes rapidly, indicating permission
to go straight as well as make a left turn in front of opposing traffic, which is
being held by a steady red lamp. (This "advance green or flashing green
can be somewhat startling and confusing to drivers not familiar with this
system. This also can cause confusion amongst visitors to British
Columbia, where a flashing green signal denotes a pedestrian controlled
intersection.) Another interesting practice seen at least in Ontario is those
cars wishing to turn left that arrived after the left turn signal ended can do
so during the amber phase, as long as there is enough time to make a safe
turn. A flashing amber arrow, which allows drivers to make left turns after
giving way to oncoming traffic, is becoming more widespread in the United
States, particularly in Oregon. In the normal sequence, a protected green
left-turn arrow will first change to a solid amber arrow to indicate the end of
the protected phase, then to a flashing amber arrow, which remains
flashing until the standard green light changes to amber and red.
• Lane control
Lane control lights are a specific type of traffic light used to manage
traffic on a multi-way road or highway. Typically they allow or forbid traffic
to use or more of the available lanes by the use of green lights or arrows
(to permit) or by red lights or crosses (to prohibit).
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• Dummy lights
A dummy light is a traffic light which stands on a pedestal in the middle
of an intersection. There are at least three which still operate in the United
States today, all located in New York State: Beacon, Canajoharie and
Croton-on-Hudson. There have been number of requests in recent years
for these traffic lights to be removed due to safety concerns, but the historic
values have kept these landmarks at their original.
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A semaphore
London, 1868
The first known signal device for
regulating street traffic was
installed in 1868 in London, at the
intersection of George and Bridge
Streets near the Houses of
Parliament. Designed by railroad
signal engineer JP Knight, it had
two semaphore arms which, when
extended horizontally, meant
“stop”; and when drooped at a 45-
degree angle, meant “caution.” At
night, red and green gas lights
accompanied the “stop” and
“caution” positions (Sessions 1971;
Mueller 1970).
By the signal “caution”, all persons
in charge of vehicles and horses
are warned to pass over the
crossing with care and due regard
to the safety of foot passengers.
The signal “stop” will only be
displayed when it is necessary that
vehicles and horses shall be
actually stopped on each side of
the crossing, to allow the passage
of persons on foot; notice being
thus given to all persons in charge
of vehicles and horses to stop clear
of the crossing.
Proclamation of Richard Mayne,
London Police Commissioner, in
1868; quoted in Mueller 1970
uc-iyk
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A traffic tower in Detroit
Detroit was a hotbed of innovation for traffic signals. In 1917, Detroit installed the first traffic tower in the United States at the intersection of Woodward Avenue and Michigan Avenue. In 1920, Detroit became the first city to use red, green, and yellow lights to control traffic. And a Detroit police officer named William L. Potts invented the 4-way, 3-color traffic signal.
uc-iyk. 2010