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31-12-2010, 03:13 PM
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speed cameras.ppt (Size: 2.65 MB / Downloads: 120)
Speed cameras were introduced in west London in 1992 and following their success in reducing speed related crashes and injuries their use expanded to many other areas of Great Britain. The equipment is expensive to buy, operate and maintain and their support in prosecution procedures also much substantial administration costs. However and the cost are small compared to the benefits of society and the economy.
NEED OF SPEED CAMERA
Although there is good road safety performance, the number of people killed and injured on our roads. So the roads safety strategy was published or introduced to support the new casualty reduction targets. The road safety strategy includes all forms of invention based on the engineering and education and enforcement and recognizes that there are many different factors that lead to traffic collisions and casualties. The main reason is speed of vehicle. We use traffic lights and other traffic manager to reduce the speed. One among them is speed cameras.
Speed cameras are recommended under use to reduce road casualties. Since these cameras save lives of road users the speed camera is also known as" safety cameras".
Speed camera uses the basic principle of Doppler Effect and RADAR technologies.
A radar uses electromagnetic waves to detect objets and provide informations about them (distance, speed).
The radar sends radio waves (electromagnetic waves) at a given frequency and listens for their return (echo). If an object is in the beam, some waves will bounce off it and return to the radar. By dividing the time it took for the waves to travel back and forth by the speed of the waves (the speed of light) it is then easy to determine the distance.
To determine speed, radars use the doppler effect. They measure and scale the frequency variation between the radio wave sent and the radio wave received (echo). If the object is moving away, the frequency will be lower, if it is getting closer, the frequency will be higher. Depending on how much lower or higher the echo frequency is, it is possible to know at what speed the object is moving from the radar position.
The principle of this effect is well known in the study of sound.If the source of sound, emitting a note of frequency ‘f’ is move with a constant velocity 'V' relative to an observers, it is found that the observers p Perceives a sound having the frequency f' which differs from ‘f', being greater or smaller according to the source is move towards or away from observers. This phenomenon in sound was first explained by Doppler and hence the name Doppler effect.