The Mystery Of Traffic Lights
Ever wondered how traffic signal lights work? Sometimes, they change at the darndest, most inconvenient and seemingly arbitrary times. Other times, they’re amazing – they seem to “know” you’re coming and turn green for you just before you have to stop.
The fact is, signals work in several different ways, depending on where they are. In most large metropolitan areas, most of them on on timers. The reason is there’s usually traffic 24/7. On the other hand, in suburban and rural areas where traffic ebbs and flows – or in left turn lanes (right turn lanes if you’re in Great Britain or Japan) – various types of sensors are used.
Laser sensors and rubber pneumatic hoses are used frequently, but the most common mechanism is an inductive loop. An inductor consists of a coil of wire, which builds up a magnetic field. The coil keeps current from flowing to the electrical device – in this case, the light bulb in the signal – until the magnetic field is fully formed. Once this magnetic field is in place, the current can flow normally.
By putting more iron in or near the inductor, the amount of current is reduced because of raised induction levels. Since an automobile contains a substantial amount of iron, it’s presence over a coil increases induction – thus inhibiting the flow of electricity to the red light. (Ah! Another mystery solved…)
Ever wondered how traffic signal lights work? Sometimes, they change at the darndest, most inconvenient and seemingly arbitrary times. Other times, they’re amazing – they seem to “know” you’re coming and turn green for you just before you have to stop.
The fact is, signals work in several different ways, depending on where they are. In most large metropolitan areas, most of them on on timers. The reason is there’s usually traffic 24/7. On the other hand, in suburban and rural areas where traffic ebbs and flows – or in left turn lanes (right turn lanes if you’re in Great Britain or Japan) – various types of sensors are used.
Laser sensors and rubber pneumatic hoses are used frequently, but the most common mechanism is an inductive loop. An inductor consists of a coil of wire, which builds up a magnetic field. The coil keeps current from flowing to the electrical device – in this case, the light bulb in the signal – until the magnetic field is fully formed. Once this magnetic field is in place, the current can flow normally.
By putting more iron in or near the inductor, the amount of current is reduced because of raised induction levels. Since an automobile contains a substantial amount of iron, it’s presence over a coil increases induction – thus inhibiting the flow of electricity to the red light. (Ah! Another mystery solved…)