I tried google. I tried Jeeves. I tried the SD archives. I could swear I saw this somewhere, but I can’t find it now or remember the answer.
My SO heard somewhere that flicking your car’s headlights from low to high beam changes traffic lights from red to green. We have taken to walking at first light and we have to drive a few miles to get to a good place, so it’s still dark while she’s driving.
She drives me bonkers blinking her lights when we hit a red traffic light. She even backs up sometimes and then goes forward to take another run at it. She sometimes quickly changes lanes back and forth, saying sometimes that works, while looking like a drunk driver.
I beseech her to stop, saying that when it “works” it’s just coincidence. To no avail.
Does anyone have the answer? (Jesus,what if she’s right. I’ll just have to grit my teeth, waiting for her to back into someone, or for a cop to give her a sobriety test.)
I have never heard of a traffic signal based on headlight brightness, that’s for sure.
However, the notion of backing up and “taking another run at it” does have a sound basis. Some traffic signals will not change for one vehicle. At those types of intersections, backing up will sometimes fool the sensor into thinking another car has arrived and is waiting. This sometimes is sufficient to trigger the cycle.
And sometimes the sensors are bad, or have a very narrow focus. I have one intersection I go through every single day like this, on a small side-road. I can sit forever, unless I pull up with my car in just the right position. If I do so, then the light changes in 5 to 10 seconds. If I don’t, it stays red until I move.
But the vast, vast majority of lights do not have bad sensors. It’s all coincidence. And a friend of mine, an ex-traffic engineer (Civil), assures me that it is all coincidence - you will not able to replicate the flash that is on top of the fire trucks.
Ummm. . . If she still believes that it works after she has disproved her own theory, what makes you think she’ll believe anything this board has to offer?
I’ll tell you what will make a red light change though: When you see a red light, slowly count to 100,000. The light will change – usually before you reach 100,000. Works every time!
Some traffic lights have sensors that are triggered by strobe lights (i.e. very bright, very fast* flashes of light, which cannot be duplicated by manually flashing your hi-beams).
They give a green light to emergency vehicles as they approach the intersection, which is safer than the EV going through a red light (even with lights and sirens blazing.)
Traffic Lights can work in a number of different ways:
Some have pressure plates, these suck for riders on motorbikes as they pretty much have to wait for somebody else to come along to trigger it for them.
Some work on timing, these go off at set intervals. If a crosswalk is present, then it may or may not also change to walk unless somebody presses the button facing in the proper direction. In these cases hitting the crosswalk button will NOT change the light any faster then it would otherwise go, it just enabled the Walk light the next time the traffic signal changes to the appropriate phase.
Some lights are also connected to the cross walk button so that when somebody presses the cross walk button the traffic light also changes very soon afterwards. These are quite a bit rarer (at least in my city).
Some lights use other miscellaneous sensoring technologies, but in general the ones listed above (timing, or a pressure plate) are the major ones.
Quick strobe lights that are used to on /some/ lights to indicate an emergency vechical is passing and to instruct the light to change from red to green, but they are not going to be simulated by head beam level hi beams. No chance, sorry.
Driving erratically like that IS a good way to get hit though, especially if somebody comes up behind you quickly or is just flicking around a turn, when they might have otherwise had space to stop, with you backing up you run into them, and liability claims get really confusing.
That and why is she in that big of a hurry to go on a walk? Really now, if somebody cannot enjoy the peace and tranquility of an early morning city, then I do think that the person is losing out on a lot of what early morning walks can give besides just exercise.
Rest assured that the strobe light system is not going to be that easy to spoof.
I don’t know the specifics of them, but if I were designing such a system I would encode the flashes in some way. The simplest would be to only respond to flashes of a certain frequency. So you might have to flash at exactly 14 flashes per second or something in order to make it work.
BUt nothing would stop a determined hacker from setting up a light sensor and measuring the flashes from an ambulance (best place to set up - right outside the EMS department garage), and then building a device to mimic it.
So, I might get a little trickier. Perhaps the strobe has to flash 5 times in the first second, then twice in the next second, then 7 times in the third one in order to ‘trigger’ the system. That could also be hacked, but not as easily.
If I wanted to make it even tougher, and I had stop lights with real time clocks in them, I might set up an algorithm that requires a different set of coded flashes by the hour, and day of the week.
Lots of other possibilities. Having seen these things in action, it looks to me like it’s a straight, constant-frequency strobe. The city relies on laws against using your own strobe to deter people from gaming the system. After all, if you put a strobe on your car bright enough to trick the lights, it’s also bright enough for any cop within a few blocks to see it.
For what it’s worth, the sensor is just a loop of wire buried in the road. Cars driving over the loop change the electrical properties around the wire (increasing the capacitance to ground.) Pressure sensors fail too easily and would require tearing up the road whenever they need to be replaced.
Or what is used as a trigger itself may involve Ultra Violiant or very low Infra Red lights and you’d have one hell of a time setting up the system yourself.
Just having the sensor triggered to pick up a pulse, say whatever the morse code is for SOS, (or even just one letter, the simplier the better, I would go for binary myself) would also likely work.
Think TV remote control. Think of how bleeming hard those first (few) generation “Universal Removes” where to get working.
Now imagine not having a handy dandy test box to play around with to see if you have hit upon the right frequency yet. Or in this case pattern.
Why assume it is the main siren strobe light on top that is doing the job, an array of LEDs attacked to the top of the ambulance would not be noticed behind any of those front plate reflectors that are on everything else, and since it is the pulse of the light that you would mostly be interested in. . . . though certainly a clear piece of plastic could be put over in front of the LEDs in order to ensure that wavelength is not changed if you want to go that route as well.
Thanks everyone. At last, ammunition. Barb just read this and she didn’t throw anything at the screen. A good sign. We’ll see if this makes a difference, Dr. Matrix. At least I can stop yelling,“Coincidence!”
Also, some of the systems that use the strobelight make all the lights turn red. That’d be a good frat-house prank, but it won’t get you to your destination any faster.
Whelen is one of the biggest manufacturers of emergency vehicle lighting. Visit the Whelen Automotive Page and click on “3M Opticom” for an example. Unfortunately, I don’t see any technical explanations to go along with it.
The traffic lights aren’t tripped by an ordinary strobe light. If they were, the lights would change every time a tow truck rolled up.
Your SO could consider outfitting her car with this system, but it would be costly and also unlikely to work at every intersection, not to mention illegal and unfair to other drivers.
I’ve been hearing about this system for a few years now, but I haven’t heard any information on how widely used it is.
My not be a help. I used to work installing electrical gates for Buisnesses and gated communities.
Most of the systems we installed had a default bypasss for emergancy vehicles. (police, fire, ambulance) It detected the frequency of the sirens.
They of course, would be difficut to set up to detect a strobe.
I have to say here in my town I have not noticed ANY lights here change when approched by a lit up emergancy vehicle. This might be because of the age of most of the traffic light systems used here.
This previous thread goes into pretty good detail about how Opticom works. The link from 3M isn’t as good as it once was, but it still gets the point across.
