Well, just about every know it all person in my town seems to subscribe to the theory that Police and Fire have the ability, at the press of a button, to alter the traffic lights so they go green in the direction they are going in.
I personally find this hard to believe, if it is true, I would estimate it to be RF that is the technology they are using, yet I am yet to be able to locate any form of antenae on any traffic lights. There is a chance that it could be underground, but I suspect that is not the case. Furthermore, there needs to be a good deal of distance between when the lights would be triggered, they can not do it only moments before the intersection, or that would not give other cars time to react, and there would be much potential for accident.
I do think that there is the ability to control the lights at the intersection nearest to the firestation, as I have seen that in action, or at least seen lights change in a fashion that lead me to think it was more than just the usual timed change.
Also making me suspicious of it being some form of RF, is that those frequencies are pretty easy to operate on, even from gadgets at your local shack, and if out of public ranges, a trip to your local garage based hobbyist can usualy remdy that.
So, if there is some control over the matter, what is the technology, and if not, then please let me know, I am reallu hoping that there are a few firefighters here than can jump on this one.
I remember reading about this some years ago. I’m not sure if has been implemented or if it is widely used.
The real problem I see is that it isn’t a “fail-safe” system. I.e. if the link doesn’t turn the light green in plenty of time, or at all, the fire truck would come barreling into a crowded intersection.
So the only safe thing would be for the engine to proceed with caution which is the way it is done now. In that case you don’t need the link.
This most certainly exists. It works on the principal of infra-red, just like your televisions remote control. The sensor is located usually (but not always) on top of the traffic light. The transmitter is on top of the emergency vehicle, usually mixed in with the red/blue lights. When the emergency lights are activated, the transmitter comes on also. It usually appears as a “quick-flash”, like a cameras flash bulb. With the red/blue lights also flashing you probably don’t notice it.
Most of these are now set up to turn all the lights red, not green. This way, all traffic stops and the emergency vehicle drives around. Another reason is because folks were using engine timing lights to change lights to green.
There’s also the system where the emergency vehicles radio in what lights they need switched to the dispatcher who then flips the lights to red. I think that’s an older system which is gradually being phased out, however.
look like the current modern way is via Opticon Traffic Control Device
which is about as far as I can get on google, no specs or other info can be found in a quick search.
It’s called Opticom, not Opticon, that could be the root of the google problem.
Opticom is a wonderful system produced by those friendly folks at 3M. You can tell if a traffic signal has an Opticom receiver by looking for a 6" tall black cylinder (about 3" across) with a 1" diameter tube (about 3" long) sticking out of it at a right angle towards traffic; sitting on top of the cross arm holding the actual red-yellow-green light sets. There may also be a white strobe light atop the arm.
Here’s how it works:
Emergency vehicle with an Opticom transmitter (a particular strobe light on the front of the truck) heads towards the intersetction.
Opticom receiver sees said light.
Signals in all directions turn yellow/red.
White strobe light on top of the signal flashes (if you have that option), letting you know the Opticom saw you and is changing signals.
Signal for the emergency vehicle turns green.
Emergency vehicle passes through intersection, everything goes back to normal.
If vehicles are approaching from two directions at once, the Opticom will set one to green and the other to red. So if you’re approaching the intersetion and you see the white strobe flash, but the light is red, another truck is coming through (be nice and stop for it).
The system can also have priorities set into it, if you want a fire engine to have priority over a police car, it will set the police car’s signal red and the fire engine’s green.
Not only does my town (Bremerton, WA) have this system, they have also put it on the city transit busses as well. The way that they are set up here is that they turn all lights red except the direction that the emergency vehicle (or bus) is traveling in.
They also have an emergency system in place that can control traffic lights from a central location, but they only use that in the case of something like a high speed chase, as a way of keeping people out of the way of the oncoming cars. In the nine years I’ve lived here, I think they’ve used this twice. There are actually revolving red lights at some of the major intersections that come on when this is activated.
The busses only can use the system if they are falling behind schedule.
Exactly perfect. The system runs on a strobe light. Just a reminder, not all emergency vehicles are equiped with this system. (If I could ever get my ambulance company to cough up the cash)
Hmph! Neat. Where I live, emergency personel approaching intersections have to turn on their sirens and hope that all the other drivers in the area have the common sense not to get in the way (and, unfortunately, the other drivers don’t always have the common sense).
Whenever we would come to a traffic signal late at night, we would flash our brights at it to make it change. You had to do it while you were still some distance away, but that was perfect because it would turn green right as you got up to it.
Oh yeah, this might be illegal or dangerous, so you shouldn’t do it.
There are bus-activated lights here in Sydney. There are several intersections in the city centre which have “Bus Only” lanes. There is a sign there saying something to the effect of “State Transit Buses only. Driver-activated signals. Cars will face long delays”.