# Traffic lights and IR lights



## kyazh (Apr 2, 2007)

This might sound like the siliest thing ever. But it was just a thought. I read somwhere online, that traffic lights have IR sensors which detect emergency vehicles thus changing the light from red to green. If a setup of a few IR LED's were aranged in a flashing pattern similar to that on an ambulance, would the traffic light switch colors? This is probably illegal and stuff, but its mainly for curiousity reasons.


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## greenlight (Apr 2, 2007)

I have never seen a light change for an emergency vehicle. They are supposed to slow at intersections, but they don't have to stop for red.


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## sideman7 (Apr 2, 2007)

I'm not sure how this works, but there was a big issue here in Las Vegas with these devices that change the lights... Here, emergency vehicles do have some device that can change traffic lights when they get close. And somehow a bunch of other people got their hands on these devices so they could blow through lights at will. The police were threatening to arrest people caught with them (although I'm not sure how they would catch you). I've seen them in action, both with ambulances and some clown with the trigger. The light will turn green for about 2 seconds then switch yellow, red. REAL annoying if you are sitting in traffic (especially since most lights here have 6 cycles).


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## Sigman (Apr 2, 2007)

It's a *Federal crime* to mess around with them...


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## beebee58 (Apr 2, 2007)

Each City has it's own set of "SOP's" reguarding traveling thru intersetions. As well as there are MANY types of "Light Block" control devices. 
As far as "slowing down", ALL city require that the P/F unit "proceed thru the intersection with due reguard", if that means STOP... you will stop. Running with "lights and siren" does not give you the right to kill someone.
Some citys SOP's state that all P/F units can only travel 5 mph over the posted speed limit. And by doing so the "unit" assumes the responsibility, there bye protecting the city. (CYCA--- Cover Your City's A_ _) 

Some older systems are controled by the dispatcher and are "called for" by the Police/Fire units. They lock up a group of lights (usually 4-8). When the lights are "locked" all 4 sides turn red.
Others are controled by the "sound" of the siren, some are controled by the "lights". 

The "newest" group is the "IR" type, how they work is not really a subject that should be disscussed on a public forum. 

Just remember that the Police/ Fire units that use them are doing so to help the public and by you yourself trying to defeat them are in violation of the law and in reality endangering the public's safety and lowering the public's confendence of the public safety officer. 


Sorry about being so long winded,
BB


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## StevieRay (Apr 2, 2007)

http://www.themirt.com/


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## Lmtfi (Apr 2, 2007)

Valuable advice: Don't even THINK about doing this.


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## qip (Apr 2, 2007)

universal remotes can change lights

but i doubt it works


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## RAF_Groundcrew (Apr 2, 2007)

The system (or more correctly, one of the more widely used systems) is called 'OPTICOM' by 3M, it uses pulses of IR light to alter the phasing of suitably equipped traffic signals as the emergency vehicle approaches.

There are 2 modes, one allows the lights to remain at green, if they are already green, the other 'forces' a green for the emergency vehicles direction, and 'reds' all others at the junction.

One mode uses 10hz, the other 14hz, if I remember..

Read more here: http://solutions.3m.com/wps/portal/3M/en_US/Traffic_Safety/TSS/Offerings/Product_Catalog?PC_7_0_56OU_root=GST1T4S9TCgv&PC_7_0_56OU_output=html&PC_7_0_56OU_gvel=PFJZV1PKJ1gl&PC_7_0_56OU_vroot=1PGXVVLN9Xge&PC_7_0_56OU_node=W7MPSPH3XVbe&PC_7_0_56OU_theme=tss_portal&PC_7_0_56OU_command=AbcPageHandler


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## StevieRay (Apr 2, 2007)

Double post deleted


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## StevieRay (Apr 2, 2007)

qip said:


> universal remotes can change lights
> 
> but i doubt it works



That is a bunch of BS!

Not nearly enough power and it has to be at approximately 14Mhz.

Don't believe everything that you see on Boob Tube!


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## carbine15 (Apr 2, 2007)

The IR signals should turn all the lights red.. that way noone can use them to get through a red light.. Around here if you run a red light they take your picture and mail you a ticket.


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## lpcmidst128 (Apr 2, 2007)

I've never seen traffic lights change from red to green when emergency vehicles approach. So its likely not very widely used yet. I'm guessing its has to be some special remote transmitter on the emergency vehicles and the traffic signals have the receiver.

I believe some transit buses have something that holds the green light (opticom?). So when they accelerate from a bus stop they don't have to suddenly stop.


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## StevieRay (Apr 2, 2007)

lpcmidst128 said:


> I've never seen traffic lights change from red to green when emergency vehicles approach. So its likely not very widely used yet. I'm guessing its has to be some special remote transmitter on the emergency vehicles and the traffic signals have the receiver.
> 
> I believe some transit buses have something that holds the green light (opticom?). So when they accelerate from a bus stop they don't have to suddenly stop.



I have seen them in action before. Here is a better explanation of how they work:

Explanation of Traffic Signal Preemption

The normal operation of any traffic signal controlled intersection is designed for the maximum and efficient throughput of vehicular traffic.

Unfortunately, a common occurrence at any intersection is traffic back-up, which can require many signaling cycles to clear. Without the ability to change the operation of the traffic signals themselves, police and emergency response vehicles can also be forced to sit in traffic, thus dramatically increasing their response times to crime scenes and fire or medical emergencies.

Furthermore, even without heavy traffic, a police or emergency response vehicle entering a traffic signal controlled intersection at a high rate of speed places all motorists (and sometimes pedestrians) at extreme risk.

Traffic signal preemption is an optical communications system that allows preemption-equipped vehicles to alter the normal operation of preemption-equipped traffic signals.

An overview of a typical scenario is as follows:

A fire truck is dispatched to an emergency.

The fire truck is equipped with multiple emergency warning lights and a siren… The fire truck is also equipped with a preemption transmitter, which, in operation, is a high intensity forward-facing strobe light that is flashing at a rapid rate - much faster than normal attention-getting lights on the fire truck.

When the fire truck approaches within 1,800 feet (line-of-sight) of a preemption-equipped traffic signal controlled intersection, the preemption detector (normally mounted on the cross-arm that suspends the traffic signal) "sees" the fire truck’s preemption transmitter and locks onto its flashing strobe.

Once the traffic signal "sees" the fire truck, it begins to initiate a "preemption sequence" of the actual traffic signal that is different from normal operation.

If the fire truck already has a green light, the light will remain green. Any other direction that also has a green light (usually the opposite direction) will first get a yellow light, then red.

When all of the other directions are then red, and the fire truck’s direction is the only one that is green, the left turn arrow will illuminate (if one exists), and a brilliant white flood lamp mounted near the traffic signal will begin to flash. This flood lamp tells the driver of the fire truck that he now has control of the intersection, and complete right-of-way.

If the fire truck has a red light, any other direction that has a green light will transition to yellow, then red. When all the directions (including the fire truck’s) are red, the traffic signal facing the fire truck will then turn green, along with the left turn arrow (if one exists), and the brilliant white flood lamp will begin to flash.

Once the fire truck has passed through the intersection, optical communication with the preemption detector (on the traffic signal) is lost. At that time the traffic signal will default back to normal operation. Conversely, until the fire truck passes through the intersection, it will have a green light, regardless of the time duration.

If several intersections are within the 1,800 foot range of the fire truck’s preemption transmitter, they will all respond accordingly to the above operational description.



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## Art Vandelay (Apr 2, 2007)

I wonder, how many red lights would you have to skip to balance out the six month sentence this carries. How long does the average red light last?


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## dalekcommander (Apr 3, 2007)

We installed these OPTICOM's on our ambulances a few years back. They work great - if you are approaching an interection equipped with a sensor.
When the first unit was in we only had to wait minutes before the next Code-3 call came in(this is L.A.).
The driver made it from just about one end of the city to the other in about 3/4ths of the normal time it would have taken.
When he returned to the station we asked, "Well? How'd it work?"
He promptly answered, "Dunno. Everytime we got to the intersections the light was green."
I wanted to be the first to crack him one upside his brain bucket, but someone beat me to it.

Some traffic lights respond to white-light strobe functions as well. I tried this at night with the handheld spotlight in my ambulance and the damn thing worked! Once. May have been a fluke.


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