12-05-2011, 04:35 PM
PRESENTED BY
AZEEZ OLAREWAJU LAWAL
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CHAPTER 1
INTRODUCTION
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 the United Kingdom, 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.
The operation of standard traffic lights which are currently deployed in many junctions, are based on predetermined timing schemes, which are fixed during the installation and remain until further resetting. The timing is no more than a default setup to control what may be considered as normal traffic. Although every road junction by necessity requires different traffic light timing setup, many existing systems operate with an over-simplified sequence. This has instigated various ideas and scenarios to solve the traffic problem.
To design an intelligent and efficient traffic control system, a number of parameters that represent the status of the road conditions must be identified and taken into consideration.
1.1 Background History
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 first 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. These include:
(i) Lester Wire, a Salt Lake City policeman who set up the first red-green electric traffic lights in 1912.
(ii) James Hoge, from Cleveland, who in 1914 designed some red-green electric lights with a buzzer which sounded when the lights changed.
(iii) William Potts from Detroit, who designed the first three-colour electric traffic lights in 1920.
(iv) John Harriss, a Police Commissioner from New York who developed the first interconnected three-colour electric traffic lights in 1922.
(v) 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]. This optimization is done using the Programmable Logic Controller (PLC).
1.2 Problem Definition
The aim of this project is to design a program for Programmable Logic Controller(PLC) that could minimize the waiting time of the cars at intersections, when the trafficvolume is significantly high. Besides that, it can prevent the emergency car stuck in thetraffic jam at the intersections as well.
1.3 Objectives of Project
1. To understand the structure and operation of PLC
2. To study the ladder logic design and their programming technique
3. To understand how to make the interfacing to the PLC
4. To design a program that works together with a model of four- junction traffic light and sensors.
5. To build the model of four-junctions of intelligent traffic light that can overcome some of major problem of current traffic light.
1.4 Project Scope
1. Construct a model of four way junction of a traffic light model.
2. Programme a ladder logic diagram to control the traffic light.
3. Combine the software part and the hardware part to simulate a traffic light system.
1.5 Thesis Outline
Chapter 1 is the introduction to traffic light systems. This chapter also explains about project objectives and scopes and discuss about problem statement.
Chapter 2 will describe all techniques, the theory and concepts behind Traffic Lights and PLC automation. All requirements and preliminary design details will be explained in this chapter. The practical design will be discuss later in Chapter Three.
Chapter 3 focuses on hardware development and configuration. This chapter explain every detail about PLC FESTO FEC FC34and traffic light model. The wiring diagram forthis hardware also will be discussed in this chapter.
Chapter 4 deals with the software development using FESTO Software Tools FST 4.10 Programmer. These chapters also discuss the flowchart and development programfor traffic light systems.
Chapter 5 presents all the results obtained and the configuration of doing simulation in the real world.
Chapter 6 discusses the conclusion of this project, the development of traffic lightcontrol system using Programmable Logic Controller. This chapter also explains theproblem and the recommendation for this project and for the future development orsystemmodification.
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
Traffic signals are the most convenient method of controlling traffic in a busy junction.But, we can see that these signals fail to control the traffic effectively when a particular lane has got more traffic than the other lanes. This situation makes that particular lane more crowdy than the other lanes. If the traffic signals can allot different time slots to different lanes according to the traffic present in each lane, then, this problem can be solved easily.
2.2 The Basics of British 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 the UK, 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.
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 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.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 lights and are clearer and more energy-efficient. It is estimated that replacing all the traffic light bulbs in the UK with LEDs would save enough energy to power the city of Norwich.
2.21 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 in the UK, although it is not illegal to jaywalk, doing so violates the Highway Code and those responsible are liable for any resulting accident. Those using pedestrian crossings on side roads have right of way over vehicles once they have begun to cross [1].
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 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 sighted 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.
Vehicle Detection Systems is either Inductive loops or sensors or Video detectionsystem.For the last two decades most traffic lights at busy intersections and pedestrian crossings have been controlled by ‘inductive loop’ sensors. Normally seen as dark square outlines on the road surface, they detect a passing vehicle by using a magnetic field to detect the metal components in the passing vehicle. They then send information on location and speed to the computer controlling the traffic signals.
The inductive loop system however has a number of important drawbacks, firstly is that they are often easily damaged by road degradation, utility works or road maintenance and secondly the need to close a section of road to install the system and its associated wiring, both inevitably increasing costs and congestion.
Although the 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 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.
• 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.
