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INTRODUCTION
Although there is good road safety performance the number of people killed and injured on our roads remain unacceptably high. 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 on the side of urban and rural roads, usually placed to catch transgressors of the stipulated speed limit for that road. The speed cameras, the solely to identify and prosecute those drivers that pass by the them when exceed the stipulated speed limit.
At first glance this seemed to be reasonable that the road users do not exceed the speed limit must be a good thing because it increases road safety, reduces accidents and protect other road users and pedestrians.
So speed limits are good idea. To enforce these speed limit; laws are passed making speed an offence and signs are erected were of to indicate the maximum permissible speeds. The police can't be every where to enforce the speed limit and so enforcement cameras art director to do this work; on one who's got an ounce of Commons sense, the deliberately drive through speed camera in order fined and penalized .
So nearly everyone slowdown for the speed Camera. We finally have a solution to the speeding problem. Now if we are to assume that speed cameras are the only way to make driver's slowdown, and they work efficiently, then we would expect there to be a great number of these every were and that day would be highly visible and identifiable to make a drivers slow down.
Speed cameras are invariably hidden behind trees, road signs and often the first indication that one is passing through a speed camera point is the ruler marks painted on the carriageway or flash of the camera that it goes off.
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.
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. We can discuss the Doppler Effect in these speed cameras and other working in these cameras.
INTRODUCING THE DOPPLER EFFECT
The device that is the first generation RADAR is not capable of determining the speed of the detected object. This was limited to measuring the movement of echo on the screen, which gave a rather inaccurate result.
As an example consider the car that makes a sound with a fixed frequency. When you are in the car, you won't notice any variation in the frequency of the engine sound. However you stand at the side of the road and listen to the car when it drives past under identical condition you will notice that the frequency of the engines sound increases as the car comes nearer and then decreases as the car travels past you.
It is a matter of common experience that the pitch of the note appears to change when either source or observers or both are in motion relative to each other. Either the source or the observers or both move relative to and each other, the apparent pitch produced by the sounding body appears to be higher than actual pitch. In the same way, when the source moving towards the observers or the observers moving away from this source or both moving away from each other the apparent pitch will appear to be lower than the actual pitch of the sounding body. The apparent change in pitch due to relative motion between source and observer is known as the Doppler's principle.
For example: if a railway engine moving fast with its whistle blowing is approaching an observer, the pitch appears to become more. The pitch of the note appears to become less just as the engine moves away from the observer on the platform.
Doppler Effect: the principle of this effect is well known in the study of sound. It is known that if the source of sound, emitting a note of frequency 'v' is move with a constant velocity 'V' relative to an observers, it is found that the observers p Perceives a sound having the frequency v' which differs from 'v', 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. But Fizeau showed that the same effect on light. Thus if the source of light is
moving with a wavelength observed in the Spectroscope slightly different from the original wavelength.
The principle of speed camera that is the Doppler's effect can be described by the formula
fM= 2vfEcos(α/c)
Where
FM if the frequency of the received signal
v is the speed of vehicles
fE if the frequency of transmitted signal
α is the angle between the transmitted signal and path along which the vehicle travels
c is propagation speed of the signal in the air.