how do traffic lights work?

Question

i'm just really curious.. how do they work?? how do they time the lights so precisely..?? when a car comes, the light turns green, when there are no cars it turns red. how does this work??

just curious :]

Answer 1

there are sensors under the asphalt that tell the central computer at every stop light that there are cars waiting usually at the left hand turn lane and the lights are timed by a rotary switch that tells the computer how long to keep them green and red usually is different depending on which road its on major roads have longer greens than minor roads these waits can be changed day by day or hourly

Answer 2

Some are on simple non-intelligent timers, set by traffic engineers who have studied traffic patterns in that area. Some are more sophisticated and the timers change during certain times of the day to account for rush hours and nighttime hours. Others are even more intelligent and detect when cars are passing or waiting for the light, which affects the timing. Some are even more sophisticated and are synchonized with other lights along a highway to keep traffic flowing smoothly at speed-limit speeds.

Intelligent light control systems are more expensive and are therefore not within the budgets of some cities, especially small towns, but many large cites as well. Most simply have crude timers.

Answer 3

Traffic lights are controlled by computers which are set at certain " phases " at different times of the day which controls priority, timings as well as light durations, and more. There are squares cut in the lanes at the intersection as well at consistent distances on the approach. Wire is " looped " in these sqaures, and when energized, they create a magnetic field. When the metal of a vehicle passes over the loop, it breaks the magnetic field and creates a signal to the computer. That is why it is important to pull up to the line, at an intersection, if you want the light to change in your favour.

Answer 4

Some are set up on phases. For an area that has heavy traffic during certain hours they have one program then at night when there is less they have a different program. Others have sensors so when cars pull up at the red then it will let it know to change.

Answer 5

They are controlled by one of two methods. The first (more common) is computer controlled from a central location. This system permits timed light changes that keep traffic moving smoothly and is most often used in big cities.

The second, less common method is the one that uses individual sensors to change the lights. If the light chnages every time you approach the intersection, chances are it is controlled by sensor. Good luck!

Answer 6

How does a thermos bottle work---you put in hot it stays hot---put in cold it stays cold---how does it know Actually traffic lights don't work at all. People work traffic lights operate.

Answer 7

There's a computer controlling it.

Answer 8

traffic lights are set on timers that can be adjusted they alternate all the time wether there's any traffic or not
sequence is red ,.red amber, amber, amber green ,
green,green amber ,amber red

Answer 9

Elves

Answer 10

by electricity