Traffic light control

[moe]

Can anyone tell me how a traffic light control works? In town they changed the lights so when a emergeny fire or police car pass with there lights on they get the right of way . Is there a rate ,frequency or cycle that the light strobe flashes? a tow truk went by with it's strobe lights on and the lights did not change.Thanks for any help.

[Chris Smith]

A small device atop the light pole that looks like a small camera sets it off to change the lights in favor of the emergency vehicle. <p>Sound, light, or radio waves encoded do the trick. <p>Each city may use different means, but all three methods are supposed to be uniform?

[Dean Huster]

The ones I've seen are triggered by a low-power radio signal on the emergency vehicles and bring the entire intersection to a full red-light-on-all-the-time stop in all directions, rather than in favor of the emergency vehicle. This allows the emergency vehicle safe access to the oncoming lanes for travel through the intersection. To do the latter would make for a very messy detection system and possibly wouldn't allow for some odd variations in traffic patterns through the intersection.<p>Dean

[dacflyer]

i work in traffic signals here... its called pre-emption...some use a strobe flashing at a certain frequency, and kelvin color..almost impossible to homebrew...
also some use radio signals...depends on the city..most are all on different frequencys...and are trunked frequencys now
they are integrated with their 2 way radios<p>the ads you see in magazines.. don't work...lol
we have tested them...

[dacflyer]

oh,, by the way...tow trucks are not considered emergency vehicles..only fire / rescue / ambulance
are..