The ongoing traffic light dilemma...

Myself, having never been or ever knowing anyone employed by the D.O.T. or any of the companies contracted to install traffic lights, am wondering.........

Do they actually use PLC's to control the lights?

I would imagine there would have to be a "traffic light controller" or something a little more application specific, and I'm sure using a "regular" PLC would also introduce safety issues.


This is a completely un-researched post........I'm just curious.

duh

They have to be controlled by PLCs. How else would you explain all of the posts. Also, these projects are usually given to the lowest bidder, usually to companies with little to no PLC support.

Duh, haven't you been paying attention. lol

The question that I have never been able to answer is:

HOW DO THEY GET THE LIGHTS TO TURN RED EVERY TIME MY CAR APPROACHES?

Knowing grins aside, I've not worked on any DOT-related equipment except some MicroLogix on radiomodems that control the avalanche control warning signs at Snoqualmie Pass.

Eagle Signal is the only brand name I can recall seeing associated with traffic control systems. I see their name cast into control cabinet housings on lots of traffic light systems I've examined while loitering.

I once got involved in a lumber stacking machine for which we purchased an Eagle Signal micro-PLC as a low-cost controller. While I'll give them the benefit of the doubt as this was eight years ago, the little thing wasn't worth the plastic in it's case. Huge trouble keeping an analog input stable, and noise faults if you looked at it funny, and a DOS editor that... eew.

I don't think it's made anymore. A company called Eagle Signal is owned by Danaher and makes timing relays, but the traffic control company is owned by Siemens and is called Eagle TCS.

I'll stop my bike tomorrow by the control cabinet on 65th southbound onto I-5 and start taking apart the control cabinet... let's see how long it takes the patrolmen to show up !

Not wanting to show up on the evening news myself, I am in awe of Ken's dedication! Could this even hit CNN?

I expect there are lots of approaches, but I'm pretty sure traffic lights are controlled by their own market specific controllers. I do know traffic lights get their power and signals from a separate set of wiring buried under our streets. They don't just tap off normal utility power. And unlike our beloved student exercises, in all but the smallest bergs they aren't independent. Most cities try to synchronize lights or else operate them from a central controller to smooth traffic flow. I also know that this was already going on in the sixties, before Mr. Morely created a convenient way for professors to develop the ubiquitous traffic light exercise.

How else could they get them to turn red every time ganutenator comes along?

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Beleive it or not, guys, I have actually worked on real traffic lights.

City of Baltimore, 1989.

It was my first project in this field, and I didn't know what a PLC was. I was hired as a tech writer, so my knowledge is limited, since I had nothing in my past to relate it to. But...

No PLCs were used. Traffic lights have their own speciallized circuit boards, deidicated to the task. Lots of vendors, models, and options, depending on how 'intelligent' you need them to be.

That project involved having a set of VAX minicomputers to communicate whith each of these stand-alone units, to assist in the coordination of the lights (so that if you drove at just under the speed limit, you would not get stopped at every intersection).

The units have their own diagnoses, able to tell when a bulb is out (and to report it downtown - also part of the project).

They have some local control, so that someone with a key (to open the panel) and a 1 hour training course, can set the things to blink red all-ways, or red one way and yellow another.

And so on.

But I'm always ammused that my very first exposure to the automation industry, was with the traffic light problem.

Trying to keep Ken out of the hoosegow

After Allen's post I had to do some searching and find out some more about these things. I came up with this site.

http://www.eagletcs.com/

Unfortunately, they don't have a ladder logic posting! Sorry students, you'll still have to work for it.

(Note to friends outside the US: Hoosegow is Amercian slang for jail - or gaol if you choose - and comes from the Spanish juzgar meaning "to judge".)

I'd be surprised to see a PLC installed on a traffic light anywhere but NYP. Traffic lights were invented way before PLCs, and it's one of those industries where things tend not to change once there's a working model (does anyone want to see my new design for a stop sign).

If it ain't broke... Slap a PLC on it?

AK

Yes there are almost as many different traffic light control
models as there are PLC models the first ones were nothing like a PLC
and very specialized in what they did. But as with all things they
are evolving to some logic control similer to a plc.
OH ya I have had some experence with traffic light controller
but in no way an expert.

Re Ken Moore in hoosegow

Ken if you are bound n determined to get into one of those cabinets I would not recommend the one on 65th entry - very conspicuous - unless you are bound n determined to go visit hoosegow. When you do get arrested please make sure you get charged in Seattle Municipal Court.

They have a very good web page capability to enable me to keep track of your case. I have first hand knowledge and have learned being involved with the courts and our legal system is a royal PITA - and I am just the victim - I have no desire to gain first hand knowledge about being the charged - but if you insist well,,,,,,,

Dan Bentler

Please check the dates on the OP -- this thread is ANCIENT!!

Traffic Light Recycling

OZEE said:

Please check the dates on the OP -- this thread is ANCIENT!!

Click to expand...

OZ
Yes the original posting is as old as the hills but look at the benefits
1. We have not had a traffic light posting in quite a while
2. This one is old and is being recycled - recycling is the rage now is it not?
3. Good opportunity to razz Ken Roach

Dan Bentler

Something I've always wanted to know is does flashing your lights at temporary traffic lights make them change any quicker or is it just a myth?

I know certain lights here have strobe detectors on them for fire engines. They start changing as soon as they detect a strobe at the right frequency. One of those situations where its good to hang back 50 feet from the fire engine and just cruise along.

Marshy, Christoff; Just investigated this myth since my wife was insitant that it worked. Yes a strobe will change some of the older systems, however you would have to flash your light at something 80pls/sec. Some newer systems are encoded and IR. BTW I found the simple logic to verify if it worked or not, if it worked your light would be green, all others will be red, and no walk signals. Gee I knew that would be 3hrs well spent someday.