HomeDiscussion ForumHow does traffic light work? Is there an A.I. consciousness at work?

How does traffic light work? Is there an A.I. consciousness at work?


  1. No AI is at work. Just simple timing circuits with detection interrupts. Some lights have a predefined timing so that the lights are cycled through the 3 colors for all streets intersecting at that control light. The process can be interrupted by a vehicle coming to a light on a side street and is detected as being there. Then the interrupt is made and the light goes red for one traffic direction and green for the vehicle that just came to the light. Some traffic lights are controlled by a central control system that is computer based, but can be over ridden by a person at the control station.

  2. Traffic light control comes in many flavors.
    The basic traffic control is just a sequencer with several timers. This means that the lights will go through a sequence of events with the same times every time. These can include left and right turn light, crosswalk light, no turn on red lights, ect.
    Sometimes, it’s beneficial to adjust the timing for the time of day. More traffic might go down one route in the morning then back on another. The times that the green is given can be adjusted accordingly.
    Most people don’t know this, but many lights have sensors that detect a specific frequency of light flashing. On the front of many emergency vehicles, there are flashing lights. There may be many on some but one that flashes at the correct frequency. When the circuit detect the emergency vehicle, the controller can interrupt the sequence and give the emergency green and everybody else red. After a certain time after the signal is gone, the lights will return to normal operation.
    Crosswalks sometimes have buttons which indicate to the controller that a pedestrian wants to cross. Their operation is pretty straight forward. Press the button and in some time the light will signal you to cross.
    One of my favorite topic concerning traffic is I.L.Ds. These are Inductive Loop Detectors. These can often be seen with a good eye. Their telltale indicator is a rectangle, square, or diamond cut into the pavement. It is usually filled in with a black tar. Under the tar is loops of wire used to form the inductive loop. I.L.Ds are often found in left turn lanes with a left turn light. They are found in many places on busy streets. They are usually used for automatic gates for exiting vehicle and to keep the arm from coming down on a car. They also are used as traffic detectors on highways. They can nearly instantly tell if traffic gets backed up.
    An inductive loop detector can “see” if there is a big chunk of metal above it because it effects the inductance of the loop. With a special detector card, the changes to the high frequency waveform that drives the I.L.D is detected. The result is a signal which indicates if a vehicle is over the inductive loop.
    The basic application for an I.L.D is to switch a light for a waiting car. This way, the main route can keep green if there isn’t any cross traffic. Also if a car is under a gate, the gate will stay up.
    Slightly more advanced applications for turn signals and other light timing is adjusting to conditions. The route with the heavy traffic can be set actively to get longer green light time for the particular lights. If there is no signal, the left turn lane might be green for 5 seconds in case the I.L.D fails. If the signal indicates the many cars are waiting to turn, it could stay green for say up to 15 seconds. Heavy left turn lanes often have two loops for better control.
    Two inductive loops a given distance apart can detect the speed of vehicles. The time between when the first turns on and the second turns con can be calculated into speed.. These are often used on congested highways and roads to detect traffic conditions. These can also be used for more advanced traffic control.
    The most advanced traffic control is a large area network. These are used for very congested roads and highways. The communications line is usually buried fiber optics.Some have lights restricting vehicles from entering a highway. There are also stretches of road that have many, many light that are all controlled together. The later could be a highway off ramp onto a busy road to a stadium or other high traffic venue. The number of lights could severely restrict that traffic flow. I.L.Ds with some clever timing can increase the capacity of the road by a good amount.
    So called “fuzzy logic” can be used to attempt to determine the best timing off of the time of day, and I.L.Ds. Basically this simply weights in various options and attempts to find the best.
    Programmed controllers are sometimes said to be “intelligent.” They are really just dumb with a clever program written to them but they do appear pretty smart when they do stuff right.

  3. I wanted to say what a good answer from Marc, although fuzzy logic…………I don’t think so. I would have to suggest traffic lights are all rule based logic. Its subjective as to if this constitutes AI.
    Also, while all the things he described are possible, most are not used and we still waste millions of hours and pump tons of CO2 into the atmosphere stuck at a stop light when there’s no-one to go.

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