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# "Smart" Stoplights

hook all those dumb stoplights up to a super-computer.
 (+13, -1) [vote for, against]

You know what I can't stand? It's when you're at a red light and, once it turns green, the light at the next block turns red. Most stoplights are either on a timed cycle, or have one of those detectors to tell it when there's a car waiting. A few are even timed so that if you're going the speed limit you should theoretically hit all green lights. They're all incredibly inefficient, and probably waste millions of years of human life each year. It would be a relatively small investment to hook all the lights up to a grid connected to some sort of "super-computer" (or maybe just a SGI workstation). If all the lights were equipped with detectors the computer would know where the traffic is, and it would be able to calculate the most efficient stoplight sequence for that specific moment. You'd still have to wait at red lights, but at least you'd be wasting less of your life.

Anyone know exactly how much time people waste at stoplights?

 — flapmaster, Dec 14 2000

(?) SCOOT http://www.scoot-utc.com/whatis.htm

xkcd's "Long Light" http://xkcd.com/277/
is xkcd a 'baker? [Gamma48, Jun 06 2009]

GPS traffic solution GPS_20taken_20to_20logical_20conclusion
GPS traffic solution [marquisdenet, Jun 08 2009]

Yes, but this is a fiendishly difficult problem for typical street geometries. Even ignoring cross street traffic, imagine a single street with irregularly spaced stoplights. How do you sequence them so there is a "pulse" of green lights in _both_ directions? It can often be done, but it's not easy; I believe a full grid (or arbitrary graph) solution is NP-complete (very hard for large grids). This also reminds rmutt of an adolescent discovery that lights sequenced for 30 mph are also sequenced for 60 mph, 90 mph, etc., as long as they are regularly spaced.
 — rmutt, Dec 14 2000

 Australia has had this for 16 years and has exported it to many other countries including the UK. The USA has never been interested in our product though.

 Our traffic lights are connected in regional clusters where each intersection votes and 'marries' and 'divorces' nearby intersections according to statistical patterns.

 The regional cluster controllers work independently but are also linked to a central system in the city where they can be adjusted.

 When a major sporting event finishes, the closest intersections will adjust their cycle timings and also notify other nearby intersections.

 When I visited the traffic control centre in the city, the engineer intentionally mucked up the timing of a large intersection to show us how quickly the statistical algorithms in the system were able to iron out the traffic jam he caused.

 A recent Australian study found that SCATS saved 20% in travel time, reduced the number of stops by 40%, and resulted in a 12% reduction of fuel consumption.

 S.C.A.T.S. Sydney Co-ordinated Adaptive Traffic System

 (The only thing the Roads and Traffic Authority [RTA] won't do [despite my numerous proposals] is connect all this data to the web so I can plan a good time to head to work or to head home)

http://www.its-australia.com.au/article.htm
 — goodie, Dec 15 2000

 rmutt's post on timed lights brings back fond memories of late night runs through Wilmington, DE's 35 MPH timed signals.

I really think we (Americans) ought to scrap the whole signal thing and go to round-abouts! Saves time AND electricity!
 — wasraw, Dec 15 2000

...I'm trying to get my hands on that "Opticon" system: the gadget fire department rigs have which temporarily changes red lights to green. Did I just leak this? Great. Just great...
 — iuvare, Dec 15 2000

On roundabouts Vs lights: Philosophically speaking, roundabouts work on a Socialist ethic – they require everyone to police their own rights of way and to offer the right of way to someone else when the rules say so. Lights are equivalent to the State saying you will stop, you may go. Knowing how Communism goes down in much of The States, I'm not sure roundabouts are your answer. Nowadays, larger roundabouts in the UK have traffic lights on them to cope with the traffic volume. What does this say about the state of society? Have you seen the havoc computer-controlled lights cause in the Italian Job?
 — Wire-Fu Man, Dec 16 2000

 Ah, the communist theory of round-abouts works well in the U.K. where folks are quite polite and civilized about queues and right-of-way. However, round-abouts can be utilized in a very non-communist "imminent domain" way as I've seen illustrated in the Mediterranean countries. I believe that Americans would quickly grasp and accept several right-of-way principles I've seen on small roads in areas south of Rome:

 1) Velocity Rules 2) Maneuverability will save your a** 3) When in doubt, he with the most mass wins!

I think the current combination of road-rage and large SUV's will lend themselves to a much richer driving experience in the US if we implemented round-abouts!
 — wasraw, Dec 16 2000

 While visiting Ireland, I enjoyed driving through the roundabouts there, and thought they were a very smooth way to design an intersection (New Jersey has them also, and they are the one and only good thing about driving in New Jersey (which I try to avoid whenever possible (New Jersey, that is... not the roundabouts))). That being said, Philadelphia has a very large roundabout-type area by the art museum which I find almost impossible to navigate for some reason.

[wasraw: are you a Delaware native?]
 — PotatoStew, Dec 17 2000

PotatoStew: Not native. Spent my middle and high school years there, then left. "Small Wonder!"
 — wasraw, Dec 19 2000

 I like "Immanent Domain." We should make that a Political Topic, somewhere supra.

 Why not go vertical? Stacked freeways everywhere, with control lights for merges. Only not here in shaky California.

 I remember 4-way stops working absolutely smoothly in the '50's. That was before EVERYONE was SO IMPORTANT. I didn't know we were so socialist. We thought it neighborly, civil. Now, we may never recover from the '80's.

The Australian voting system we now know would not work in Florida, etc.
 — rfalv, Dec 31 2000

Australians........
 — cletusboy, Dec 31 2000

We need to eliminate cars and put in bike paths. You may also drive your golf carts on the path. You may ride a horse on the path. Your feet are welcome on the path. But cars will not fit. We do not need the pollution. Someday they will be planting flowers on the highway. The bicycles will avoid trampling them.
 — Vance, Jan 29 2001

The following lights are green.....green lights, yellow lights....lights that have been red less than 5 seconds and lights that have been red over 20 seconds......
 — Susen, Feb 09 2001

i live in england and i think roundabouts work fine and i don't think its cos everyone wants to be nice to eachother its just that most people dont pullout in front of moving vehicles because its stupid and they will get the blame for not giving way to the right
 — edski, Feb 21 2001

Susen: In Sao Paulo, Brazil, red lights actually are often treated as green after about 11:00 p.m., because the risk of getting hit in the intersection is less than the risk associated with stopping the vehicle (e.g., carjacking, etc.).
 — beauxeault, Feb 21 2001

Roundabouts can also be a pain. If you encounter one after another after another, they get quite tedious after a while and your passengars don't like the side to side motion much either. It's true though, they're generally quicker than stop lights and stop signs.
 — mgrant, Apr 15 2001

 There are two main problems with roundabouts:

 1)They only really work if the traffic flows on each arm are relatively similar.

 2) They take up a lot more space than a signal junction, which is a problem in cities.

In London, as well as many other UK cities a 'smart' system like this is used called SCOOT (see link). Induction loops set in the carriageway feed information back to a central computer, which can then alter the signal timings accordingly. A common problem with this system in operation is that the loops are frequently damaged - usually by utility companies digging up the road. Also, there are a lot of junctions that don't have them installed yet, and, quite frankly, creating more capacity for traffic on the road is not really seen as a top priority; more money is being spent on, for example, detecting approaching buses and giving them priority at signal junctions.
 — stupop, Mar 04 2002

 Well, New Jersey does have some interesting traffic oddities. There are a lot of traffic circles, which most people from other parts of the country despise. Better are the many many intersections where in order to turn left or make a U turn, you must turn right a block or two before the intersection, so that you can approach it from the perpendicular direction.

 We also had a lot of traffic circles in the Boston area, which is home to the best drivers in the U.S. The three rules above are what we went by, alright. Plus of course that you could never exhibit fear while driving; you always had to seize the advantage! I often think fondly of the days when I would commute to work on Storrow Drive, at 80mph, in bumper to bumper traffic, or driving along the shoulder on Route 128 to avoid cars that were in the actual lanes.

New Jersey's alright, but it's no Boston or Rome.
 — cpt kangarooski, Mar 05 2002

 — mighty_cheese, Mar 06 2002

 I'm not sure I like the idea of the massive central computer. Microprocessors are very cheap. Big computers are not. So why not put a micro at every intersection. Have it linked up in a network with all other nearby intersections, if any. This would work for all types of intersections, including those outside of the big city traffic grid. Each intersection could negotiate with surrounding intersections for optimum flow. And you could still communicate with a central site if necessary.

 It seems to me that the biggest problem is the sensor. I would think the underground metal detector type sensors would be the most reliable and least affected by weather or other factors.

 Motorcycles and maybe some cars might fail to be detected. So I would suggest that the system have a minimum and maximum hold time for each direction. That way, an undetected vehicle would only experience a delay rather than never getting a green.

Another time a smart traffic light would be nice is late at night when there is no one on the road but you. Don't you hate it when a light turns red just as you approach and there are no other cars anywhere to be seen?
 — willatlguy, Mar 13 2002

 You know, the traffic management is perfect project for neural computering. I like the idea putting a processor at each intersection and monitoring the traffic volume for input and time of signal change as output. Moving traffic is positive feedback, stopping traffic as negative feedback. With the network of processors connect to each other, someone might develop an alogrithm that allow the whole system to balance itself to an optimum performance. The beauty about neural network is that if part of it break down like a street close or something, system automatically adjust and compensate without human interference.

I do not think anyone here is an expert on neural network. It would be interesting to take a look to it.
 — bing, Mar 14 2002

Been done.
 — simonj, Jul 17 2003

most metropolitan areas ALREADY HAVE THIS. one step further, they also have cameras watching the traffic to spot accidents and speed reaction times by emergency personnel
 — Aphyllophorales, Jul 17 2003

//lights sequenced for 30 mph are also sequenced for 60 mph, 90 mph// - this is only true for very special cases of temporal & spatial spacing, while 60s lights driven with 30 are easy.
 — loonquawl, Jun 07 2009

To prevent the side to side motion of a roundabout is simple. Just make it all straight lines for those who wish to go straight, then use little feeder angled lines for those wish to turn. Kind of like a tic tac toe grid.
 — marquisdenet, Jun 08 2009

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