Top Banner
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
30

Traffic Light

Sep 05, 2014

Download

Documents

Uche Iyk

Chapter One
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Page 1: Traffic Light

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

Page 2: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

2

® Info @ 08034117423 & [email protected]

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.

Page 3: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

3

® Info @ 08034117423 & [email protected]

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.

Page 4: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

4

® Info @ 08034117423 & [email protected]

DESIGN, CONSTRUCTION AND TESTING OF

HARDWARE IMPLEMENTATION OF INTELLIGENCE

TRAFFIC LIGHT CONTROL CIRCUIT

FEBRUARY, 2010.

Page 5: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

5

® Info @ 08034117423 & [email protected]

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.

Page 6: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

6

® Info @ 08034117423 & [email protected]

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

Page 7: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

7

® Info @ 08034117423 & [email protected]

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

Page 8: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

8

® Info @ 08034117423 & [email protected]

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.

Page 9: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

9

® Info @ 08034117423 & [email protected]

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

Page 10: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

10

® Info @ 08034117423 & [email protected]

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

Page 11: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

11

® Info @ 08034117423 & [email protected]

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

Page 12: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

12

® Info @ 08034117423 & [email protected]

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

Page 13: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

13

® Info @ 08034117423 & [email protected]

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.

Page 14: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

14

® Info @ 08034117423 & [email protected]

• 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

Page 15: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

15

® Info @ 08034117423 & [email protected]

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.

Page 16: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

16

® Info @ 08034117423 & [email protected]

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

Page 17: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

17

® Info @ 08034117423 & [email protected]

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

Page 18: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

18

® Info @ 08034117423 & [email protected]

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.

Page 19: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

19

® Info @ 08034117423 & [email protected]

• 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

Page 20: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

20

® Info @ 08034117423 & [email protected]

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

Page 21: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

21

® Info @ 08034117423 & [email protected]

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

Page 22: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

22

® Info @ 08034117423 & [email protected]

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

Page 23: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

23

® Info @ 08034117423 & [email protected]

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,

Page 24: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

24

® Info @ 08034117423 & [email protected]

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

Page 25: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

25

® Info @ 08034117423 & [email protected]

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

Page 26: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

26

® Info @ 08034117423 & [email protected]

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

Page 27: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

27

® Info @ 08034117423 & [email protected]

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).

Page 28: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

28

® Info @ 08034117423 & [email protected]

• 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.

Page 29: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

29

® Info @ 08034117423 & [email protected]

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

Page 30: Traffic Light

Do you know that sensibility leads one to productivity? February 15, 2010

30

® Info @ 08034117423 & [email protected]

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