Post by thread:Traffic Lights (Was Car LED lighting etc ...)

Boy, this must be the longest thread I've seen. OK, some posters were talking about air traffic control, collision avoidance etc. Here's a question re traffic control. In Australia, Melbourne suburbs, lots of traffic lights seem to be synchronised so that heavy traffic flow on a main road gets all green lights. I always assumed it was done with simple timers. However, I'm *told* that radar detectors - you know those little black-box gizmos you put on your dash to defeat the police? - are set off when approaching these synched lights. ('Course that's only what I've been told. Heh! Well, I wouldn't use illegal technology myself, naturally ..............!) So, are synched traffic lights controlled with a microwave system somehow? Just wondering. PJH

>only what I've been told. Heh! Well, I wouldn't use illegal technology myself, >naturally ..............!) Radar detectors illegal? In the US, you can own and operate any sort of receiver you desire, no problem. Federal law. (Just don't key the mike unless you are licensed in some manner.) Some states, such as Virginia, think they don't have to obey the FCC on that one. If I were still there, I'd almost like to take it to the Supreme Court. But I don't speed, and never owned one. Andy ================================================================== Andy Kunz Life is what we do to prepare for Eternity ------------------------------------------------------------------ spam_OUTandyTakeThisOuTrc-hydros.com http://www.rc-hydros.com - Race Boats .....andyKILLspam@spam@montanadesign.com http://www.montanadesign.com - Electronics ==================================================================

I know that here the major roads have traffic lights that communicate with radio. You see the occasional antenna on top on the light pole, or near to the light box. -Adam PJH wrote: > > Boy, this must be the longest thread I've seen. > > OK, some posters were talking about air traffic control, collision avoidance > etc. Here's a question re traffic control. > > In Australia, Melbourne suburbs, lots of traffic lights seem to be synchronise d > so that heavy traffic flow on a main road gets all green lights. I always > assumed it was done with simple timers. However, I'm *told* that radar detecto rs {Quote hidden}> - you know those little black-box gizmos you put on your dash to defeat the > police? - are set off when approaching these synched lights. ('Course that's > only what I've been told. Heh! Well, I wouldn't use illegal technology myself , > naturally ..............!) > > So, are synched traffic lights controlled with a microwave system somehow? > > Just wondering. > > PJH

Not quite, IIRC radar detectors are illegal in some states. They aren't allowed to pull you over if they suspect you have one, though. Only if they notice it during another infraction of the law. -Adam Andy Kunz wrote: {Quote hidden}> > >only what I've been told. Heh! Well, I wouldn't use illegal technology > myself, > >naturally ..............!) > > Radar detectors illegal? > > In the US, you can own and operate any sort of receiver you desire, no > problem. Federal law. (Just don't key the mike unless you are licensed in > some manner.) > > Some states, such as Virginia, think they don't have to obey the FCC on > that one. If I were still there, I'd almost like to take it to the Supreme > Court. But I don't speed, and never owned one. > > Andy > > ================================================================== > Andy Kunz Life is what we do to prepare for Eternity > ------------------------------------------------------------------ > andyKILLspamrc-hydros.com http://www.rc-hydros.com - Race Boats > .....andyKILLspam.....montanadesign.com http://www.montanadesign.com - Electronics > ==================================================================

At 11:11 30/07/99 +1000, you wrote: >Boy, this must be the longest thread I've seen. > >OK, some posters were talking about air traffic control, collision avoidance >etc. Here's a question re traffic control. > >In Australia, Melbourne suburbs, lots of traffic lights seem to be synchronised >so that heavy traffic flow on a main road gets all green lights. I always >assumed it was done with simple timers. However, I'm *told* that radar detectors >- you know those little black-box gizmos you put on your dash to defeat the >police? - are set off when approaching these synched lights. ('Course that's >only what I've been told. Heh! Well, I wouldn't use illegal technology myself, {Quote hidden}>naturally ..............!) > >So, are synched traffic lights controlled with a microwave system somehow? > >Just wondering. > >PJH > > Are, uhm NO. Sync traffic lights are via telephone lines (Also provides communications to the signal control centre) (Notticed how the "In case of faults call 131360 and quote this number" sign is gone?) This is so for the city area as it allows VIC roads to alter sequences during heavy traffic times. Dennis

Andy Kunz wrote: > > >only what I've been told. Heh! Well, I wouldn't use illegal technology > myself, > >naturally ..............!) > > Radar detectors illegal? > > In the US, you can own and operate any sort of receiver you desire, no > problem. Federal law. (Just don't key the mike unless you are licensed in > some manner.) > > Some states, such as Virginia, think they don't have to obey the FCC on > that one. If I were still there, I'd almost like to take it to the Supreme > Court. But I don't speed, and never owned one. > > Andy > Further erosion of our rights, Andy. Virginia is NOT the only state to ban speed trap receivers ... and the feds ban receivers capable of hearing the 800MHz cell phone frequencies. Thomas Jefferson must be turning over in his grave! - Nick -

At 21:19 29/07/99 -0400, you wrote: {Quote hidden}>>only what I've been told. Heh! Well, I wouldn't use illegal technology >myself, >>naturally ..............!) > >Radar detectors illegal? > >In the US, you can own and operate any sort of receiver you desire, no >problem. Federal law. (Just don't key the mike unless you are licensed in >some manner.) > >Some states, such as Virginia, think they don't have to obey the FCC on >that one. If I were still there, I'd almost like to take it to the Supreme >Court. But I don't speed, and never owned one. > >Andy > >================================================================== >Andy Kunz Life is what we do to prepare for Eternity >------------------------------------------------------------------ >EraseMEandyspam_OUTTakeThisOuTrc-hydros.com http://www.rc-hydros.com - Race Boats >andyspam_OUTmontanadesign.com http://www.montanadesign.com - Electronics >================================================================== > > Yep, here we can not have K band detectors in a car Dennis

>Further erosion of our rights, Andy. Virginia is NOT the only state I know. It was the only one I'm familiar with, though. I would still love to press the issue, though. >to ban speed trap receivers ... and the feds ban receivers capable of They only banned manufacture. They didn't do anything until the Newt got caught that time on one. >hearing the 800MHz cell phone frequencies. Thomas Jefferson must be >turning over in his grave! I know. Andy ================================================================== Andy Kunz Life is what we do to prepare for Eternity ------------------------------------------------------------------ RemoveMEandyTakeThisOuTrc-hydros.com http://www.rc-hydros.com - Race Boats spamBeGoneandyspamBeGonemontanadesign.com http://www.montanadesign.com - Electronics ==================================================================

You know, since we've meandered quite OT <s>. I'll sorta bring back around. I've often sat at traffic lights during heavy traffic and thought about how adding a little intelligence to the system could help minimize traffic. But even such a seemingly simple task can get complicated when you consider other lights adjacent to each other. Then you would need someway of analyzing congestion in all four directions, etc. It would an interesting project and after reading this thread (including what you wrote below), we might not be that far off from AI traffic lights. Eric On Thursday, July 29, 1999 8:44 PM, Dennis Plunkett [SMTP:TakeThisOuTdennisEraseMEspam_OUTRDD.NECA.NEC.COM.AU] wrote: > At 11:11 30/07/99 +1000, you wrote: > >Boy, this must be the longest thread I've seen. > > > >OK, some posters were talking about air traffic control, collision avoidance > >etc. Here's a question re traffic control. > > > >In Australia, Melbourne suburbs, lots of traffic lights seem to be > synchronised > >so that heavy traffic flow on a main road gets all green lights. I always > >assumed it was done with simple timers. However, I'm *told* that radar > detectors > >- you know those little black-box gizmos you put on your dash to defeat the > >police? - are set off when approaching these synched lights. ('Course that's > >only what I've been told. Heh! Well, I wouldn't use illegal technology > myself, > >naturally ..............!) > > > >So, are synched traffic lights controlled with a microwave system somehow? {Quote hidden}> > > >Just wondering. > > > >PJH > > > > > > > Are, uhm NO. > Sync traffic lights are via telephone lines (Also provides communications > to the signal control centre) (Notticed how the "In case of faults call > 131360 and quote this number" sign is gone?) > This is so for the city area as it allows VIC roads to alter sequences > during heavy traffic times. > > Dennis

M. Adam Davis wrote: > Not quite, IIRC radar detectors are illegal in some states. They > aren't allowed to pull you over if they suspect you have one, though. > Only if they notice it during another infraction of the law. That's an interesting case regarding civil rights supposedly guaranteed by the US constitution. Aside: this country has no provision for civil rights in its constitution - probably what you'd expect for a penal colony, and a maudlin discussion current, albeit intermittent, on whether we should be a Republic, in which I have *rarely* heard civil rights discussed despite the conmmonsense that it would be the *only* valid reason to seek a republic! Anyway, as I understand it, radio receivers are a (US) Federal matter as they are here. State or local rulings on any form of restriction of radio receivers, including installation of antennae and radar detectors are automatically invalid. Well, that's how it *should* be... But as you say, the FCC chooses to assert an essentially un- constitutional ruling on 900 MHz. Fascinating! Dennis Plunkett wrote: > Are, uhm NO. > Sync traffic lights are via telephone lines (Also provides > communications to the signal control centre) I think the correct answer is "No, unless it's Yes". Whilst Telstra was a Government monopoly, civil authorities were entitled to free telecommunications services. Now they charge for lines, many services are choosing to go it cheaper and use (packet) radio links. Also: > Yep, here we can not have K band detectors in a car It appears there *may* be an exception for *licensed* K-band users, such as myself. I'm not sure how well it's been tried... Eric Oliver wrote: > I've often sat at traffic lights during heavy traffic and thought > about how adding a little intelligence to the system could help > minimize traffic. ... > we might not be that far off from AI traffic lights. We're a very long way off indeed. It's Politically Incorrect you see. Current traffic control thinking says that the slower traffic is, the safer it is. No-one can dispute this, so any effort to speed up traffic is PI. There're presently designing roundabouts to slow down traffic by making it go round complex slalom bends, putting 50 km/h zones in residential areas (including main thoroughfares), and they haven't used anticipatory sensors for Green Extension on traffic lights for many years. Don't expect traffic to get any quicker! -- Cheers, Paul B.

Dennis Plunkett wrote: > >So, are synched traffic lights controlled with a microwave system somehow? > > Are, uhm NO. > Sync traffic lights are via telephone lines (Also provides communications > to the signal control centre) (Notticed how the "In case of faults call > 131360 and quote this number" sign is gone?) > This is so for the city area as it allows VIC roads to alter sequences > during heavy traffic times. Right, so are the suburban ones also hardwired into the 'phone system? Just wondering why a radar detector would be activated at traffic lights in that case? PJH -- ************************************************* PETER HYNES FAX: Int-61-3-9809 0604 NET: RemoveMEelekTakeThisOuTnetstra.com.au WEB: http://www.netstra.com.au/~elek/ *************************************************

Andy Kunz <supportEraseME.....MONTANADESIGN.COM> wrote: > In the US, you can own and operate any sort of receiver you desire, no > problem. Federal law. (Just don't key the mike unless you are licensed in > some manner.) Didn't the Electronic Communications Privacy Act of 1986 (ECPA) bans receivers that cover the 800 MHz cellular phone band? Of course, the whole idea of banning a receiver to promote privacy is a travesty. They should have required that the cellular companies either (1) implement strong security in the communications, or (2) notify their customers that their communications are insecure. Or both! Legislating that communication is secure is about as useful as legislating that pi equals three [*], or passing a resolution that the Boston Strangler was a compassionate gentleman [**]. Eric [*] Nearly passed in 1897 by the Indiana State Legislature as House Bill #246 http://www.cs.unb.ca/~alopez-o/math-faq/node45.html [**] Texas House of Representatives, http://www.urbanlegends.com/politics/boston_strangler.html

> We're a very long way off indeed. It's Politically Incorrect you see. >Current traffic control thinking says that the slower traffic is, the >safer it is. No-one can dispute this, so any effort to speed up traffic >is PI. The other thing is the slow traffic in commercial zones increases traffic through the stores. So the merchants actually WANT the slow traffic. Andy ================================================================== Andy Kunz Life is what we do to prepare for Eternity ------------------------------------------------------------------ EraseMEandyrc-hydros.com http://www.rc-hydros.com - Race Boats RemoveMEandyEraseMEEraseMEmontanadesign.com http://www.montanadesign.com - Electronics ==================================================================

Don't try taking one into Canada either. -----Original Message----- From: Andy Kunz <RemoveMEsupportspam_OUTKILLspamMONTANADESIGN.COM> To: RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU <EraseMEPICLISTspamspamBeGoneMITVMA.MIT.EDU> Date: Thursday, July 29, 1999 9:20 PM Subject: Re: Traffic Lights (Was Car LED lighting etc ...) >only what I've been told. Heh! Well, I wouldn't use illegal technology myself, >naturally ..............!) Radar detectors illegal? In the US, you can own and operate any sort of receiver you desire, no problem. Federal law. (Just don't key the mike unless you are licensed in some manner.) Some states, such as Virginia, think they don't have to obey the FCC on that one. If I were still there, I'd almost like to take it to the Supreme Court. But I don't speed, and never owned one. Andy ================================================================== Andy Kunz Life is what we do to prepare for Eternity ------------------------------------------------------------------ RemoveMEandyKILLspamrc-hydros.com http://www.rc-hydros.com - Race Boats andySTOPspamspam_OUTmontanadesign.com http://www.montanadesign.com - Electronics ==================================================================

[snip] > even such a seemingly simple task can get complicated when you consider > other lights adjacent to each other. Then you would need someway of > analyzing congestion in all four directions, etc. It would an interesting > project and after reading this thread (including what you wrote below), we > might not be that far off from AI traffic lights. I have a friend that works with a math system dedicated to this kind of situation, is not that difficult, it uses lots of statistics and priorities. In real, the system has all the time in the world to take care of a lazy flow system... the word is "pacing"... some of them use electromagnetic sensors in the asphalt to count and feel vehicles movement, other just use statistics and synchronization... my own words about this? None of them works right! Want to see a complete mess? Track down the complete crazy tail a Firetruck create behind it after opening (at its control) all the green lights in its way... breaking all the sensible statistic traffic flow... It can take more than 10 minutes to get normal again, with luck. Wagner.

-----Original Message----- From: Gabriel Gonzalez <spamBeGonetgoSTOPspamEraseMECHIH1.TELMEX.NET.MX> To: KILLspamPICLISTspamBeGoneMITVMA.MIT.EDU <EraseMEPICLISTEraseMEMITVMA.MIT.EDU> Date: Friday, July 30, 1999 3:32 AM Subject: Re: Traffic Lights (Was Car LED lighting etc ...) >I believe they already are AI controlled, or then how would you explain >that, when it's green and you're about to arrive at the intersection it >changes to red before you can cross it, especially when you're going fast! I have seen a set of smaller loops embedded in the roadway several hundred feet before the stop light. I figure they are either checking for advancing traffic or possibly backed up traffic if the line should reach back that far.

Margo Erickson wrote: > I have seen a set of smaller loops embedded in the roadway several > hundred feet before the stop light. I figure they are either checking > for advancing traffic or possibly backed up traffic if the line should > reach back that far. Dead right on both counts. But that's to what I referred in my "Politically Incorrect" post. The use of advance or anticipatory sensors with an "extended green" cycle is self-evident, but policy has in many places swung toward using lights to *slow down* traffic unless traffic jams come to public notice. Consequently, here at least, very few suburban installations have this feature nowadays. (They *used* to though!) My town has just succumbed to PC. They are at this time busily installing "(50) Area" signs all over the place, including many of the main four-lane (two each way) thoroughfares! (Default limit 60 k/h) -- Cheers, Paul B.

At 06:45 PM 7/30/99 -0400, Wagner Lipnharski wrote: >[snip] >I have a friend that works with a math system dedicated to this kind of >situation, is not that difficult, it uses lots of statistics and >priorities. In real, the system has all the time in the world to take >care of a lazy flow system... the word is "pacing"... some of them use >electromagnetic sensors in the asphalt to count and feel vehicles >movement, other just use statistics and synchronization... my own words >about this? None of them works right! I've been at an intersection on a motorcycle where the light would not change unless a vehicle was over the buried loop. Of course I happened to be the first one in the queue, to the right of the loop, with a long line of irate drivers behind me... When I finally noticed the loop, I walked my cycle over it a couple of times to get the light to change... I kind of feel guilty as I've designed buried loop vehicle sensors for car wash systems back in the 70's... - Tom ------------------------------------------------------------------------ Tom Handley New Age Communications Since '75 before "New Age" and no one around here is waiting for UFOs ;-)

Tom Handley wrote: > I've been at an intersection on a motorcycle where the light would not > change unless a vehicle was over the buried loop. .SNIP...... When I > finally noticed the loop, I walked > my cycle over it a couple of times to get the light to change... > Yeah, the ones around Melbourne are also buried in the bitumen. One across the 'straight ahead' lanes and one in the 'right turn lane' in cases where there's a red\green arrow. (Opposite to US practice, we drive on the left.). You can tell from the scars where the surface has been cut. At intersections fitted with a 'red light camera' there's a sensor loop in the middle of the intersection to bag red-light runners. Trouble is, they also bag the poor saps who get stuck in the middle doing a right turn when it goes amber. Jus' wondering again .... what would the system would do if a car stopped over one of the loops had it's own loop mounted underneath that was fed current pulses? Maybe look like a massive traffic flow against the red light? PJH

> Jus' wondering again .... what would the system would do if a car stopped > over one of the loops had it's own loop mounted > underneath that was fed current pulses? Maybe look like a massive traffic > flow against the red light? I doubt the system would care much. I had a guided tour of the traffic light control system in Brisbane some years ago (was running on HP-1000 minis, still is AFAIK) and the thing they're most interested in is the detector occupancy, i.e. the percentage of time that something is over the detector loop. It's a direct measure of traffic density. Also, with the red light cameras, the way I was told they work is that the camera is triggered if the detector becomes unoccupied while the light is red, i.e. the standard in-lane detector is used, and it triggers the camera if a vehicle leaves the detector during the red light phase. Two photos are taken, one straight away, and one later to confirm that the vehicle did actually pass through the intersection (i.e. if you move out, then reverse back, you're ok). IOW there is no detector in the middle of the intersection. You will see detectors out in the intersection in some places, particularly where there is a right turn lane, to detect cars that have moved out into the intersection waiting for a gap. A few more red-light cameras around here would be welcome - the number of light-runners seems to be increasing. However the government seems more interested in more speed cameras, I guess they raise a lot more money. Cheers, Clyde -- Clyde Smith-Stubbs | HI-TECH Software Email: @spam@clyde@spam@spam_OUThtsoft.com | Phone Fax WWW: http://www.htsoft.com/ | USA: (408) 490 2885 (408) 490 2885 PGP: finger spamBeGoneclydeKILLspamhtsoft.com | AUS: +61 7 3355 8333 +61 7 3355 8334 --------------------------------------------------------------------------- HI-TECH C: compiling the real world.

Clyde Smith-Stubbs wrote: {Quote hidden}> > > Jus' wondering again .... what would the system would do if a car stopped > > over one of the loops had it's own loop mounted > > underneath that was fed current pulses? Maybe look like a massive traffic > > flow against the red light? > > I doubt the system would care much. I had a guided tour of the traffic > light control system in Brisbane some years ago (was running on HP-1000 > minis, still is AFAIK) and the thing they're most interested in is > the detector occupancy, i.e. the percentage of time that something > is over the detector loop. It's a direct measure of traffic density. > > Also, with the red light cameras, the way I was told they work is > that the camera is triggered if the detector becomes unoccupied while > the light is red, i.e. the standard in-lane detector is used, and it > triggers the camera if a vehicle leaves the detector during the red > light phase. Two photos are taken, one straight away, and one later to > confirm that the vehicle did actually pass through the intersection > (i.e. if you move out, then reverse back, you're ok). IOW there is > no detector in the middle of the intersection. Over on this side of the country, they use PRESSURE sensitive pads about 3 feet forward of the white line. This was proved a couple of years ago, by a group of kids that used to drop thier pants and all jump on the pad at once. Pretty funny photos.. anyway, the pads are armed when the light goes red, and 2 photos are taken, one on contact with the pad, and one a certain accurate interval afterwards... All the intersections with red light cameras now have markers painted on the road, delimiting distance, and because the two photos are accurately timed, they can infer how fast you were going at the time.. Not used for speed prosecution but useful to determine the circumstance of running the red light... ie sitting over the line, versus doing double the speed limit thru the intersection :p) Brad.......

At 08:59 PM 7/29/99 , Andy Kunz wrote: >At 09:21 PM 7/29/99 -0400, you wrote: >>Not quite, IIRC radar detectors are illegal in some states. They aren't > >The law making them illegal is illegal. The law making them illegal is just contradictory to the Act that established the FCC in 1934, which just established the fact that "if it falls on you, it is yours." However the Congress has established the fact that that they don't mind contradicting their own law, the case in point being the Electronic Communications Privacy Act (ECPA) which contradicted the 1934 law. I believe Virginia's law has survived court challenges. DC also has a similar law. Radar detectors are also banned in commercial vehicles, another contradictory law passed by the Congress (and generally ignored). The law is going to be on the side of the party that has the best lawers (cell phone companies (winners) vs. speeders, satellite companies (winners) vs. pirates, States (winners) vs. speeders). Matt Bennett

>> As I understand it over here (NZ) the radio antennas on most city traffic >> lights are to allow buses and emergency services priority - the red cycle >> can be delayed slightly. >> I've been trying to find out more details re the frequency & codes used etc. >> - but purely for academic reasons of course :-) > >It *is* a subject of absorbing academic exercise, I must agree! > >> (The antenna length suggests approx. 150MHz but that's all I've been able to >> guess so far) > >Maybe try employing a scanner? (Radio, not the image sort.) There are lists of >frequency allocations around someplace. A method that I have seen used here in the US is a system that extends the green to emergency vehicles by keying off a white strobe mounted on the front of the vehicle. The strobe frequency is specific (and unknown to me). You can spot these intersections that are suchly equipped- the optical sensor is mounted in a horizontal tube pointed along the traffic flow, attached to the same support that the light is connected to. I used to see these all over the Washington, DC area, but since I have moved to Austin, TX, I have not noticed any. Matt Bennett

Well, you could always shunt a few hundred amps through such a loop, and destroy the light controller. After a few new light controllers, they might decide to use a different method of car detection... -Adam PJH wrote: {Quote hidden}> > Tom Handley wrote: > > > I've been at an intersection on a motorcycle where the light would not > > change unless a vehicle was over the buried loop. .SNIP...... When I > > finally noticed the loop, I walked > > my cycle over it a couple of times to get the light to change... > > > > Yeah, the ones around Melbourne are also buried in the bitumen. One across > the 'straight ahead' lanes and one in the 'right turn > lane' in cases where there's a red\green arrow. (Opposite to US practice, we > drive on the left.). You can tell from the scars where the surface has been > cut. > > At intersections fitted with a 'red light camera' there's a sensor loop in > the middle of the intersection to bag red-light runners. Trouble is, they > also bag the poor saps who get stuck in the middle doing a right turn when it > goes amber. > > Jus' wondering again .... what would the system would do if a car stopped > over one of the loops had it's own loop mounted > underneath that was fed current pulses? Maybe look like a massive traffic > flow against the red light? > > PJH

Here in Orlando, it works pretty well. If the first car stops at the right position, before the perpendicular white mark (limit to stop with red light), inside the lane limits, he will be right over the sensor. What happens is that bad habit drivers just stop anywhere, over the separation white lines, ahead of the stop position, long before the "stop here" position, and then they create problems. Some drivers just stop (to gain time I think) 2 to 4 meters after the white line stop limit at red light, almost blocking the crossing flow. Even for those they installed a sensor there, so right now I can see two "8" shape sensors, one at the right position, another for those that can't break and stop where civilized people stops at red lights. There is a logic at the traffic light computer, so there are an evaluation about cars over sensors, and which flow is the one to receive the green lights at that specific moment. For example, if the crossing traffic time is expired, the computer will first open the green lights to who is waiting to do left turns, then will be the ones for trough traffic. The left turn green lights will only happens IF there is some car over the sensor, if not, it will go directly to the through traffic. I have a complain about that sensors; If I arrive over the left turn sensor less than 5 seconds before it would activate the left turn green light, and there was no other car over the sensor, the computer will not validade my car's presence and I will need to wait for a complete turn around in the flow, more than a minute with intense traffic. It looks like the computer just ignore the last 5 seconds of the sensors reading for safety or something. In Brazil they use an automatic system to monitor traffic activities on the main highways around big cities, for example S‹o Paulo city (19 million people). You can see a schematic of those highways and problems, you can even click over a specific part of it and see what heppened. It is refreshed each 30 minutes. Just for fun take a look at: http://200.19.93.5/internew/index1.html Wagner Adam Davis wrote: {Quote hidden}> > Well, you could always shunt a few hundred amps through such a loop, and destroy > the light controller. After a few new light controllers, they might decide to > use a different method of car detection... > > -Adam > > PJH wrote: > > > > Tom Handley wrote: > > > > > I've been at an intersection on a motorcycle where the light would not > > > change unless a vehicle was over the buried loop. .SNIP...... When I > > > finally noticed the loop, I walked > > > my cycle over it a couple of times to get the light to change... > > > > > > > Yeah, the ones around Melbourne are also buried in the bitumen. One across > > the 'straight ahead' lanes and one in the 'right turn > > lane' in cases where there's a red\green arrow. (Opposite to US practice, we > > drive on the left.). You can tell from the scars where the surface has been > > cut. > > > > At intersections fitted with a 'red light camera' there's a sensor loop in > > the middle of the intersection to bag red-light runners. Trouble is, they > > also bag the poor saps who get stuck in the middle doing a right turn when it > > goes amber. > > > > Jus' wondering again .... what would the system would do if a car stopped > > over one of the loops had it's own loop mounted > > underneath that was fed current pulses? Maybe look like a massive traffic > > flow against the red light? > > > > PJH

> A method that I have seen used here in the US is a system that extends the > green to emergency vehicles by keying off a white strobe mounted on the > front of the vehicle. The strobe frequency is specific (and unknown to > me). You can spot these intersections that are suchly equipped- the > optical sensor is mounted in a horizontal tube pointed along the traffic > flow, attached to the same support that the light is connected to. I used > to see these all over the Washington, DC area, but since I have moved to > Austin, TX, I have not noticed any. There are 2 strobe lights atop the ambulance, and they flash 2 times each in the course of 1 second. The pulse looks something like this: __ __ __ __ ___| |__| |_____| |__| |___ Left Left Right Right I cannot be sure of the duty cycle, but I would bet that the receiver is not that accurate. Maybe it just counts the pulses in 5 seconds.

Maybe you could get some ideas from Pee-Wee. (Sorry, couldn't resist) {Quote hidden}> -----Original Message----- > From: pic microcontroller discussion list > [.....PICLISTspam_OUTMITVMA.MIT.EDU]On Behalf Of Richard Prosser > Sent: August 2, 1999 4:03 PM > To: TakeThisOuTPICLIST.....TakeThisOuTMITVMA.MIT.EDU > Subject: Re: Traffic Lights (Was Car LED lighting etc ...) > > > Also - If I had a strobe light on my bicycle (to stop people from running > into me) that "just happened" to match the required pattern, then ..... > Richard > > -----Original Message----- > > From: Craig Lee [TakeThisOuTcleeKILLspamspamATTCANADA.NET] > > Sent: Tuesday, August 03, 1999 9:47 AM > > To: .....PICLISTRemoveMEMITVMA.MIT.EDU > > Subject: Re: Traffic Lights (Was Car LED lighting etc ...) > > > > > > Hmm.... I wonder if the sensors will respond to invisible or nearly > > invisible light.... > > > > I was in a cab once where the cab driver looked both ways carefully, > > then flicked his lights on and off at a certain rate. To my surprise, > > it worked!! > > > > Probably something you wouldn't want to get caught at, but what you > > can't see... > > > > Craig > > > > > -----Original Message----- > > > From: pic microcontroller discussion list > > > [RemoveMEPICLISTspamBeGoneMITVMA.MIT.EDU]On Behalf Of Matthew Fries > > > Sent: August 2, 1999 2:54 PM > > > To: spamBeGonePICLIST@spam@spam_OUTMITVMA.MIT.EDU > > > Subject: Re: Traffic Lights (Was Car LED lighting etc ...) > > > > > > > > > > A method that I have seen used here in the US is a system that > > > extends the > > > > green to emergency vehicles by keying off a white strobe > > mounted on the > > > > front of the vehicle. The strobe frequency is specific > > (and unknown to > > > > me). You can spot these intersections that are suchly > > equipped- the > > > > optical sensor is mounted in a horizontal tube pointed > > along the traffic > > > > flow, attached to the same support that the light is connected > > > to. I used > > > > to see these all over the Washington, DC area, but since > > I have moved to > > > > Austin, TX, I have not noticed any. > > > > > > There are 2 strobe lights atop the ambulance, and they > > flash 2 times each > > > in the course of 1 second. The pulse looks something like this: > > > > > > __ __ __ __ > > > ___| |__| |_____| |__| |___ > > > > > > Left Left Right Right > > > > > > I cannot be sure of the duty cycle, but I would bet that > > the receiver is > > > not that accurate. > > > > > > Maybe it just counts the pulses in 5 seconds. > > > > > >