stop light changing devices

[olderndirtmom]

Question to you law enforcement types and traffic engineers.

What causes traffic signals to change for alternate traffic, particularly late at night?

To be even more specific, some friends of mine are arguing the "flash your brights" method of getting signals to change faster versus the electromagnet under the pavement. One swears by the "flash your brights". The other believes that the electromagnet thing is a ruse to get people to buy a gadget they don't need, since the only information he could cull on the subject was by a company selling such a gadget.

I dutifully reported what I learned in motorcycle licensing school on the subject (electro magnet buried under asphalt). I also reported what I was instructed to do when my cycle couldn't get the signal to change (run the light)...But I wonder what you DRN sages know about the "flash your brights" thing that has been circulating since I was a child (shortly after electricity was invented) and the history of the technologies governing signal changing in the wee hours.

Any of you have inside knowledge on this subject, and the urban legends (and various snake oils) surrounding it?

 

[SpeedyManiac]

There's a weight sensor just before the stop line that triggers the lights to change. At least that's how it works up here in Canada. Look for the little metal thing stuck in the pavement a couple feet before the stop line.

 

[mmz77]

I believe it activates by a magnet which is picked up through your cars frame... At least thats what i heard.
http://www.howstuffworks.com/question234.htm

 

[Jaybird]

EMT vehicles and cops carry infrared changers.
These are sold to the public in some states.
This would have to be on top of the weight sensing or magnetic sensors that are in place at some lights.

Many times city lights, especially on one-way streets, are a timed occurrence. Set so a driver doing the correct speed can usually travel through a lot of them with no stops.
The lights on the side streets, connected to these timed avenues, are under the control of the one way streets timed lights. Unless a cop, or a mom with a new infrared toy, interrupts the flow.

 

[RM_guy]

There was a news story a while ago about some guy that was using one of those infrared changers to get to work faster. He claimed he saved 1/2 hour on the trip. Problem is it was illegal. I don't remember what the charge or punisment was but it was newsworthy!

 

[Patman]

There are several methods even within the same city, none are perfect. Some have triggers in the pavement, some timers and some a combination of both depending on time of day since traffic peaks might require different control than late at night, The IR triggers are getting installed in more locations and they are just an over ride feature for what is in place as the normal metering system.

I've heard pushing but button on an elevator multiple times makes it get there faster too but I've never seen it work.

 

[BSWIFT]

The coil of wire that is buried into the pavement "looks" for an interuption of the field, changing the induction of the circuit. This intern is connected to a timer circuit that allows the "green" light in a different direction to be turned to yellow and then red, thus giving the vehicle over the antenna a green light.
The "IR" triggers, at least here in my area, are for emergency vehicles. The sensors here locally are not InfraRed but are in the white light of the visible spectrum. The emergency vehicles are equiped with many strobes and on the front of the vehicle a set of strobes is sychronized and aimed to trigger the light. This in theory is to allow stopped vehicles to clear an intersection so the emergency vehicle does not get bogged down at the traffic lights.
I have seen the pressure sensors but they are not used in our area. This is partially due to the climate. The burried antenna has its limitations and problems that are also due to the climate. Motorcycles having less and less steel (iron) in their construction do not interupt the field sufficiently to trigger the lights. A magnet or electromagnet could help but I have yet to see it for myself. I would imagine that a 1/2" thick steel skid plate would do better than a magnet at changing the induction of the circuit. Of course this would likely way 70 lbs. It is not the weight but the iron content that disrupts the field.
If you were to place a piece of steel in the left hand turn lane, sufficient to change the induction, that left hand turn lane would get priority until it was removed. The circuit would time out but as soon as any other circuit showed normal for a few seconds, that left hand turn lane would again take priority.
A nice quaulity camera flash unit would likey trip the sensors in our area and I have witnessed several people trying it. But due to the traffic at the time, I do not know if it overrode the programmed traffic algorythems.
If you decide to try out the "flash" trick, best have your camera attached in case you are stopped. ;)

 

[Patman]

A nice quaulity camera flash unit would likey trip the sensors in our area and I have witnessed several people trying it. But due to the traffic at the time, I do not know if it overrode the programmed traffic algorythems.
If you decide to try out the "flash" trick, best have your camera attached in case you are stopped. ;)

Geesh Brian are your fingers cramped now? :laugh:

Might also be worth noting that most automobile headlights point down and are not bright enough to trigger the typically high mounted emergency triggers.

 

[FiremanCRF450R]

What we have in the city of Edmond is a system made by 3M. It is called opticom. If you look on top of our fire trucks you will see a little device that flashes like a strobe light. These devices are set at a certain frequency, and the public is not allowed to have them. They will catch the light up to a half mile away and change it green for the emergency vehicle. :nod: