How does a traffic light detect that a car has pulled up and is waiting for the light to change?
There is something exotic about the traffic lights that “know” you are there — the instant you pull up, they change! 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), or when cars have entered a turn lane (in order to activate the arrow light). There are all sorts of technologies for detecting cars — everything from lasers to rubber hoses filled with air! By far the most common technique is the 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 cut a groove in the as
