I don’t understand how they work, what they’re hooked up to and how they know when to turn from green, to yellow, to red. Are they timed? Is there a sensor, perhaps a small man hiding in the pole controlling it?
In: 7
It depends on the light. Many decades ago, they used to run on a sort of mechanical clockwork timer. These days they tend to work on Programmable Logic Controllers (PLCs) which are basically simple computers.
Depending on the needs of any given intersection, a modern traffic light might run on a simple timer (albeit digital rather than mechanical like the old days). Or, it might have sensors embedded in the asphalt to detect when there are cars stopped in certain places so that it “knows” when there’s traffic and can interrupt the timer to change to green sooner.
These sensors will typically be an “inductive loop”. An inductive loop is a loop of twisted wire. This loop is connected to a detector box which sends electricity through the wire and detects the electricity coming back. When a car passes over the loop, the presence of conductive metal (especially ferric metal) over the loop causes a change in the electrical current going through the loop, which the detector detects.
It depends on the light. Many decades ago, they used to run on a sort of mechanical clockwork timer. These days they tend to work on Programmable Logic Controllers (PLCs) which are basically simple computers.
Depending on the needs of any given intersection, a modern traffic light might run on a simple timer (albeit digital rather than mechanical like the old days). Or, it might have sensors embedded in the asphalt to detect when there are cars stopped in certain places so that it “knows” when there’s traffic and can interrupt the timer to change to green sooner.
These sensors will typically be an “inductive loop”. An inductive loop is a loop of twisted wire. This loop is connected to a detector box which sends electricity through the wire and detects the electricity coming back. When a car passes over the loop, the presence of conductive metal (especially ferric metal) over the loop causes a change in the electrical current going through the loop, which the detector detects.
It depends on the light. Many decades ago, they used to run on a sort of mechanical clockwork timer. These days they tend to work on Programmable Logic Controllers (PLCs) which are basically simple computers.
Depending on the needs of any given intersection, a modern traffic light might run on a simple timer (albeit digital rather than mechanical like the old days). Or, it might have sensors embedded in the asphalt to detect when there are cars stopped in certain places so that it “knows” when there’s traffic and can interrupt the timer to change to green sooner.
These sensors will typically be an “inductive loop”. An inductive loop is a loop of twisted wire. This loop is connected to a detector box which sends electricity through the wire and detects the electricity coming back. When a car passes over the loop, the presence of conductive metal (especially ferric metal) over the loop causes a change in the electrical current going through the loop, which the detector detects.
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