# Traffic Light Changers **URL:** \ **Category:** Factual Questions\ **Created:** [August 22, 2001, 1:26pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531 "2001-08-22T13:26:10Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Evnglion](https://avatars.discourse-cdn.com/v4/letter/e/f04885/32.png) [@Evnglion](https://boards.straightdope.com/u/Evnglion)\ **Post date:** [August 22, 2001, 1:26pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/1 "2001-08-22T13:26:10Z")
I have recently aquired a delivery-boy job, and sometimes it can be kinda stressful. I have also recently heard about, through the wonder of the internet, Traffic light changers. Evidently they are used by emergency personel, and I would think they would be illegal for civillian use. However, I have found detailed instructions on constructing a device, and it seems pretty easy. In addition to the instructions, I have found sites that actually allow you to purchase them, pre-built, and even some with a stealth shield so they are not detectable. My first question… Aren’t this illegal? If not, why? And, second, do they, or would they, actually work? ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [August 22, 2001, 1:47pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/2 "2001-08-22T13:47:08Z")
From what I understand, you just need a strobe light with sufficient brightness and correct frequency. But don’t they turn all the lights red? If so, it won’t help you at all, since you have no right to run red lights. ---
**Author:** ![jonfromdenver](https://avatars.discourse-cdn.com/v4/letter/j/82dd89/32.png) [@jonfromdenver](https://boards.straightdope.com/u/jonfromdenver)\ **Post date:** [August 22, 2001, 3:03pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/3 "2001-08-22T15:03:52Z")
no, they change the lights red in every direction except the one the strobe light is coming from and going to. but these are definately illegal for civilian use, so i wouldn’t do it. if you live in a more rural area, i’ve heard that sometimes when it’s dark outside, you can just flash your lights and hope, but that doesn’t always work i’m sure. ---
**Author:** ![Duck\_Duck\_Goose](https://avatars.discourse-cdn.com/v4/letter/d/50afbb/32.png) [@Duck\_Duck\_Goose](https://boards.straightdope.com/u/Duck_Duck_Goose)\ **Post date:** [August 22, 2001, 3:10pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/4 "2001-08-22T15:10:32Z")
Have you guys got any kind of cites for this? 'Cause Ducky ain’t buying it. 😉 Come back with your Google hit–or on it… > **[Google](https://www.google.com)** > > Celebrating the late We:wa! #GoogleDoodle I’m gonna go way out on a limb, here, E, and say that the existence of “traffic light changers” is an UL. How traffic signals work: [http://www.bikeplan.com/signal.html](http://www.bikeplan.com/signal.html) One kind works on a timer, that’s in the signal itself. The other kind is “demand actuated”–it has a wire buried in the pavement, and when a car rolls over it, the light changes. Sorry that neither of these has anything to do with a hand-held garage-door type remote control. I’ve never heard that emergency personnel can “flash” a gadget and get a light to change, either (other than in a UL context). A traffic signal is just a light bulb connected to an on/off switch and a power source; flashing a strobe light at it wouldn’t do anything at all. Here is a company that makes light bulbs for traffic signals. They’re just light bulbs (actually they’re LEDs, but it’s the same thing–a strobe light won’t make the signal change). [http://www.dialight.com/trans.htm](http://www.dialight.com/trans.htm) Here, IMO, is the source of the “you can flash a strobe at a traffic signal and it will change” Urban Legend. [http://www.tomar.com/products/sectionj/p084-5.htm](http://www.tomar.com/products/sectionj/p084-5.htm) > [@](#): > > 575R STROBEBAR LED > TRAFFIC SIGNAL INDICATOR > > This model 575R Strobebar is a strobing red signal indicator consisting of a standard 12" Dia. (30 cm) red plastic traffic signal that has a built-in white bar strobe presented horizontally across the red face. The strobe flashes at a rate of approximately once per second for as long as the red LED signal is energized. It’s an LED traffic light (bulb) that has a white strobing (flashing) stripe horizontally across it. But it’s just a light bulb, guys–it’s passive, not active. The strobe isn’t expecting anything to be flashing back at it, it’s not sending a signal back to the traffic signal itself. It’s just a light bulb. The strobing white stripe is supposed to make the light easier to see at a distance. ---
**Author:** ![Duck\_Duck\_Goose](https://avatars.discourse-cdn.com/v4/letter/d/50afbb/32.png) [@Duck\_Duck\_Goose](https://boards.straightdope.com/u/Duck_Duck_Goose)\ **Post date:** [August 22, 2001, 3:12pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/5 "2001-08-22T15:12:06Z")
And the first person who says, “Well, naturally, they’re not going to be on the Web, because they’re _illegal_, they don’t want you to know about it”, is going to be drummed out of General Questions. 😃 ---
**Author:** ![Duck\_Duck\_Goose](https://avatars.discourse-cdn.com/v4/letter/d/50afbb/32.png) [@Duck\_Duck\_Goose](https://boards.straightdope.com/u/Duck_Duck_Goose)\ **Post date:** [August 22, 2001, 3:14pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/6 "2001-08-22T15:14:58Z")
And, um, if emergency personnel _could_ “flash a gadget” and get a light to change, huccome I see all those cops and ambulances and fire trucks with lightbars going, driving through red lights? Why not just change the light? ---
**Author:** ![jonfromdenver](https://avatars.discourse-cdn.com/v4/letter/j/82dd89/32.png) [@jonfromdenver](https://boards.straightdope.com/u/jonfromdenver)\ **Post date:** [August 22, 2001, 3:17pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/7 "2001-08-22T15:17:54Z")
i can attest that i have seen with my own eyes a light turn green that i was waiting at, only for it to turn red about a second later, and a cop car with blazing sirens came through. i always thought that it was the flashing lights, but i just realized that i don’t remember what intersection i was at, and if there was a police or fire station by it. i know for sure that fire and police stations can control the traffic light closest to them from inside the building, so their vehicles can get out. so if i remember where i was, i’ll post it. ---
**Author:** ![CnoteChris](https://avatars.discourse-cdn.com/v4/letter/c/278dde/32.png) [@CnoteChris](https://boards.straightdope.com/u/CnoteChris)\ **Post date:** [August 22, 2001, 3:31pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/8 "2001-08-22T15:31:17Z")
It’s not an urban legend **DDG**. I’ve actually seen it done. I was standing on the side of a street and saw another guy using a engine timing gun- not the device the O.P. is referring to- change the lights at the end of the block. I know it changed the lights because the sensor that detects the strobe has a little light on it showing that the strobe has been detected. In all the cases I’ve seen it, the light on the strobe detector flashes a light back in the direction that the strobe came from. Kinda a confirmation message to the strobe enabled vehicle that it’s being detected. At that point, it turns all the lights in the direction the strobe _isn’t_ coming from red, and the direction of the strobe green. It’s fairly common to see in my area of Minneapolis/St. Paul. It’s also common to sit at a red light, have it go green, then immediately go red again because an emergency vehicle is approaching that light. And just to be clear, it’s not the regular rotating red and blue strobes or lights we all know of, but the white strobe kind that are attached to the light bar and pointed straight ahead towards the traffic lights. Like I said, very common in my area. Oh, and in terms of the O.P.? I’ve never heard of them, outside of the thing I saw done with the engine gun, but I bet it’s probable someone has designed a little box that duplicates that strobe. I’d also bet it’s illegal as hell too. ---
**Author:** ![Kamandi](https://avatars.discourse-cdn.com/v4/letter/k/5daacb/32.png) [@Kamandi](https://boards.straightdope.com/u/Kamandi)\ **Post date:** [August 22, 2001, 3:42pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/9 "2001-08-22T15:42:49Z")
I’m with **DDG** on this one. Let’s see some cites to back these anecdotes up. If traffic lights were switched with white strobe lights, wouldn’t lightning screw them up? ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [August 22, 2001, 3:50pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/10 "2001-08-22T15:50:27Z")
> [@](#): > > huccome I see all those cops and ambulances and fire trucks with lightbars going, driving through red lights? Perhaps not all traffic lights are equipped with such devices? > [@](#): > > wouldn’t lightning screw them up? The sensors only react to a series of flashes at specific intervals (frequency), from what I heard. ---
**Author:** ![CnoteChris](https://avatars.discourse-cdn.com/v4/letter/c/278dde/32.png) [@CnoteChris](https://boards.straightdope.com/u/CnoteChris)\ **Post date:** [August 22, 2001, 3:51pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/11 "2001-08-22T15:51:13Z")
> [@](#): > > \*Originally posted by Kamandi \* > \*\*I’m with **DDG** on this one. Let’s see some cites to back these anecdotes up. > > If traffic lights were switched with white strobe lights, wouldn’t lightning screw them up? \*\* [link deleted. this company appears to be selling to civilians devices intended to defeat the law] one I just found. It looks an awfull lot like the ones we have on the traffic semafores here. [Edited by bibliophage on 08-24-2001 at 01:25 AM] ---
**Author:** ![that\_darn\_cat](https://avatars.discourse-cdn.com/v4/letter/t/59ef9b/32.png) [@that\_darn\_cat](https://boards.straightdope.com/u/that_darn_cat)\ **Post date:** [August 22, 2001, 3:57pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/12 "2001-08-22T15:57:46Z")
'ere ya go [http://www.wattco.net/opticomemitters.htm](http://www.wattco.net/opticomemitters.htm) ---
**Author:** ![that\_darn\_cat](https://avatars.discourse-cdn.com/v4/letter/t/59ef9b/32.png) [@that\_darn\_cat](https://boards.straightdope.com/u/that_darn_cat)\ **Post date:** [August 22, 2001, 4:02pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/13 "2001-08-22T16:02:06Z")
Whoops, I ment to add… This system uses encoded infrared, so a strobe is no-go, and a computer has to validate your request, so just copying the signal seems out. ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [August 22, 2001, 4:02pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/14 "2001-08-22T16:02:35Z")
> [@](#): > > \*Originally posted by Kamandi \* > \*\*I’m with **DDG** on this one. Let’s see some cites to back these anecdotes up. > > If traffic lights were switched with white strobe lights, wouldn’t lightning screw them up? \*\* They’re real. Friends of mine in EMS have used them. [Sound activated traffic signal pre-emption systems](http://www.epsincorp.com/main.htm) products from Epsincorp. [Emergency Vehicle Traffic Pre-emption Systems](http://www.its.dot.gov/rural/module4/sld011.htm) - A slide from a US DOT report on community emergency services. [Info on strobe-light pre-emption systems](http://www.mountprospect.org/fire/trafficsig.htm). Look at google for “emergency vehicle pre-emption” or “traffic signal pre-emption” for more links. ---
**Author:** ![micco](https://avatars.discourse-cdn.com/v4/letter/m/5f8ce5/32.png) [@micco](https://boards.straightdope.com/u/micco)\ **Post date:** [August 22, 2001, 4:05pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/15 "2001-08-22T16:05:04Z")
I don’t have a cite yet, but I recall an article in 2600 a while back about the city of Dallas using remote contols to change lights for emergency vehicles. In this case, you could spoof it with a trainable universal TV remote. You had to sit at an intersection and wait for an emergency vehicle (remember this is 2600, the mag for people with way too much time on their hands). When it remoted-changed the light, you aimed your remote at the emergency vehicle and hoped to catch their signal. Once your remote was trained, you could change lights with it, but the range of the TV remotes was extremely limited, such that you might have to climb the lightpole and find the sensor to make it work (again, this is 2600, the mag for people who do because they can, not because they need to). ---
**Author:** ![CnoteChris](https://avatars.discourse-cdn.com/v4/letter/c/278dde/32.png) [@CnoteChris](https://boards.straightdope.com/u/CnoteChris)\ **Post date:** [August 22, 2001, 4:05pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/16 "2001-08-22T16:05:37Z")
Terrific link, **cat**. That’s exactly what I was referring to. And as a matter of fact, that intersection looks oddly familiar (3M–\> Minneapolis/St. Paul–\> Hmmmm…). I think that sign even says, “West Interstate 94”. That’s right up the block from me. ---
**Author:** ![Evnglion](https://avatars.discourse-cdn.com/v4/letter/e/f04885/32.png) [@Evnglion](https://boards.straightdope.com/u/Evnglion)\ **Post date:** [August 22, 2001, 4:31pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/17 "2001-08-22T16:31:48Z")
Well, I did not want to bust out the cites in the OP, but, i am getting many requests to do so, so, here it is [link deleted. this company appears to be selling to civilians devices intended to defeat the law] take a look at that. I can honestly say taht i have seen lights change all the time, and, I dunno about you guys, but it seems as though Ambulances and police cars _rarely_ have to go through a red light, it is always green. That is the main reason I think this is NOT a UL. [Edited by bibliophage on 08-24-2001 at 01:26 AM] ---
**Author:** ![Swede\_Hollow](https://avatars.discourse-cdn.com/v4/letter/s/3bc359/32.png) [@Swede\_Hollow](https://boards.straightdope.com/u/Swede_Hollow)\ **Post date:** [August 22, 2001, 6:13pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/18 "2001-08-22T18:13:34Z")
The changers are everywhere St. Paul. 3M has a major corporate campus here and they exert a lot of pressure on the local governments to have these installed. They actually experiment with new technologies on the stoplights on McKnight along their campus, they (at least used to) own some of those stoplights. It is, however, up to each city to decide if they want them. Lots of the suburbs around here don’t have them, or only have them on the major through streets. The laws that prohibit use of these changers may be different elsewhere but it is illegal for non-emergency vehicles to use the changers here. Even if it isn’t illegal where you are, do you want to risk being held responsible for an accident caused by traffic approaching a light that was green that suddenly turns red without warning (the type we have here change the lights yellow first then changes them red, like a normal light change, but some change instantly). The local paper had an article showing some police officers getting in trouble from using the changers just to avoid sitting at a long light (although I have seen them do it occasionally since then). ---
**Author:** ![Duck\_Duck\_Goose](https://avatars.discourse-cdn.com/v4/letter/d/50afbb/32.png) [@Duck\_Duck\_Goose](https://boards.straightdope.com/u/Duck_Duck_Goose)\ **Post date:** [August 22, 2001, 6:35pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/19 "2001-08-22T18:35:21Z")
Well, Huh. ---
**Author:** ![jonfromdenver](https://avatars.discourse-cdn.com/v4/letter/j/82dd89/32.png) [@jonfromdenver](https://boards.straightdope.com/u/jonfromdenver)\ **Post date:** [August 22, 2001, 6:43pm UTC](https://boards.straightdope.com/t/traffic-light-changers/77531/20 "2001-08-22T18:43:32Z")
let me take this time to gloat over the fact that i was the first to assert that these things actually do exist. hahahahahahaha. ok, i’m done. 🙂 > [@](#): > > _originally posted by CnoteChris_ > And as a matter of fact, that intersection looks oddly familiar (3M–\> Minneapolis/St. Paul–\> Hmmmm…). I think that sign even says, “West Interstate 94”. That’s right up the block from me. you live right by my girlfriend! i shoulda just called her up to verify…too little, too late… [Next page](https://boards.straightdope.com/t/traffic-light-changers/77531.md?page=2)