Traffic lights detecting a car that has pulled


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Traffic lights detecting a car that has pulled

  1. 1. Traffic Lights detecting a car that has pulled up..! Vaishnavi Chigarapalle
  2. 2. Traffic Lights • Traffic lights, also known as traffic signals, traffic lamps, and signal lights, and also known technically as traffic control signals. • These are signaling devices positioned at road intersection, pedestrian crossings and other locations to control competing flows of traffic. • Traffic lights alternate the right of way accorded to road users by displaying lights of a standard color (red, orange, and green) following a universal color code. • Green light: Allows traffic to proceed in the direction denoted. • Orange Light: Denoting prepare to stop short of the intersection. • Red Light: Prohibits any traffic from proceeding.
  3. 3. How do they detect your presence? • Some lights don’t have any sort of detectors. • For example: In a large city, the traffic lights may simply operate on timers – no matter what time of day it is, there is going to be a lot of traffic. • In the suburbs and on country roads, however, detectors are common. • They may detect when a car arrives at an intersection, when too many cars are stacked up at an intersection ( to control the length of the light). • They may also detect when cars have entered a turn lane ( in order to activate the arrow light).
  4. 4. Technologies for Detecting cars • There are all sorts of technologies for detecting cars. • They range from lasers to rubber hoses filled with air. • By far the most common technique is the inductive loop. • They can be detected using the rubber hoses, filled with air, which can be squashed by a car running over it. • Some traffic lights use a Doppler Radar module. • These use radio waves at 10GHz to 30 GHz and detect the radio waves reflected back off the vehicle. • Because they beat the received signal against a portion of that transmitted, they only detect motion.
  5. 5. • And by using quadrature receivers, can distinguish between towards and away motion. • These detectors are essentially the same as can be used to measure traffic speed. • Loop detectors can easily sense different lanes of traffic uniquely, which we can’t really do with a radar device.
  6. 6. Common Technology: Inductive Loop • An inductive loop is simply a coil of wire embedded in the road’s surface. • To install the loop, they lay the asphalt and then come back and then cut a groove in the asphalt with a saw. • The wire is placed in the groove and sealed with a rubbery compound. • We can often see these big rectangular loops cut in the pavement because the compound is obvious. • Inductive loops work by detecting a change of inductance.
  7. 7. • To understand the process, we need to look at what an inductance is. • The illustration is as follows:
  8. 8. Explanation • What we see here is a battery, a light bulb, a coil of wire around a piece of iron (yellow), and a switch. • The coil of wire is an inductor. • The inductor is an electromagnet. • If we were to take out the inductor out of this circuit, then what we have is a normal flashlight. • We close the switch and the bulb lights up. • With the inductor in the circuit as shown, the behavior is completely different. • The light bulb here is a resistor. • The resistance creates heat to make the filament in the bulb glow.
  9. 9. • The wire in the coil has much lower resistance. • So what we would expect when we turn on the switch is for the bulb to glow very dimly. • Most of the current should follow the low-resistance path through the loop. • When we close the switch, instead of getting dimmer the light first burns brightly and then gets dimmer. • When we open the switch, the bulb burns very brightly and then quickly goes out.
  10. 10. Reason for the strange behavior • The reason for this strange behavior is the inductor. • When current first starts flowing in the coil, the coil wants to build up a magnetic field. • While the field is building, the coil inhibits the flow of current. • Once the field is built, then current can flow normally through the wire. • When the switch gets opened, the magnetic field around the coil keeps current flowing in the coil until the field collapses. • The current keeps the bulb lit for a period of time even though the switch is open.
  11. 11. • The capacity of an inductor is controlled by two factors: – The number of coils. – The material that the coils are wrapped around the coil. • Putting iron in the core of an inductor gives it much more inductance. • Much more than air or any other non-magnetic core wound. • There are devices that can measure the inductance of a coil. • The standard unit of measure is the henry.
  12. 12. Example • Let’s say we take a coil of wire that is 5 feet in diameter. • This coil of wire consists of five or six loops of wire. • We cut some grooves in a road and place the coil in the grooves. • We then attach an inductance meter to the coil and see what the inductance of the coil is. • Now park a car over the coil and check the inductance again. • The inductance will be much larger because of the large steel object positioned in the loop’s magnetic field • The car parked over the coil is acting like the core of the inductor. • And its presence changes the inductance of the coil.
  13. 13. • A traffic light sensor uses the loop in that same way. • It constantly tests the inductance of the loop in the road. • When the inductance rises, it knows there is a car waiting! • So next time you are stopped at a red light and are in a hurry, try putting the car in reverse. • This helps to trip up the detector below you. • Or if we are at a traffic light that has a headlight sensor, try flicking your high beams on and off to trip the light sensor. • We never know .. We may speed up the process to getting the light to change green.
  14. 14. Sources • • • • • light.html