How does the traffic light operate?

Question

how does the rotating dashing work?

Answer 1

I am not sure what you mean by rotating dashing?  Perhaps this is just a geographic difference between us.

However, most traffic lights around here run on a simple logic program that uses sensors in the ashphault to detect the presence of cars.  These sensors are actually just a loop of wire to form an inductance coil.  You can easily see these loops as they are cut into the pavement, the coils are added, and then the pavement is patched up again.  As the car travels or stops over the loop, the inductance increases and sends the signal to the computer logic program telling it that a car is present.  Most traffic controllers will allow a certain amount of time for traffic in each direction after the presence of the car has been detected, say 1 minute of flow.

For some intersections, it is straight timer based and set to switch lights after a set amount of time, depending on how busy each street is.

So with this knowledge, you can look for the inductance coils cut into the ashphault and know where to stop your car to get and advanced green light!  (Which seems to p**s off the other drivers if you are the only car turning left!)

Answer 2

In big cities, one computer sets the timing for all the traffic lights by adjusting the program in a mini-computer at each intersection. This is done by telephone modem, like the internet. All of the computers' clock are synchronized, so they know when to change. Wire loops in the pavement act as metal detectors at some intersections; if no vehicle is in the left turn lane, the computer skips the left-turn part of the cycle. Some intersections use complex computer programs which adjust to changing traffic conditions.

In small towns, each intersection has an independent computer. It can be set to change on a regular time schedule, or it can change when a vehicle is detected over a loop of wire in the pavement.