# Do traffic light sequences ever make use of chaos in their timings? **URL:** \ **Category:** Factual Questions\ **Created:** [December 18, 2016, 7:42pm UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071 "2016-12-18T19:42:51Z")\ **Posts on this page:** 18\ **Page:** 2
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [December 20, 2016, 6:27pm UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071/21 "2016-12-20T18:27:26Z")
AFAIK traffic circles and rotaries are not the same as roundabouts. The roundabouts we have in Michigan (and that’s what we call them) are more or less identical to the ones in the UK. though some of the newer ones we’ve constructed are modified a bit; traffic turning right doesn’t always have to enter the circle at all. https://maps.google.com/maps?ll=42.5543956,-83.4487946&z=18&output=embed&dg=ntvb ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [December 20, 2016, 7:33pm UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071/22 "2016-12-20T19:33:16Z")
> [@jtur88](#): > > Closer to home, an example right here in this forum. When starting a thread, you are given space for about three words to compose a title. After three words, the first words disappear from the text entry field, so typographical errors are epidemic in threads that are otherwise more carefully proofread. The title is not seen by the poster until the thread has been posted, when it is too late to repair it without the hands-on intervention of a moderator. So,obviously, the web designer of the forum board has never actually used the product he has designed. This might be a function of your web browser. I have enough space in mine for more than 3 words, more like 6 or 8. It’s rare that I write a thread title that isn’t all in view. I’m using Firefox. > [@bump](#): > > . > I’m personally surprised that the streetlights in a city aren’t starting to be networked, so that if the cameras/inductive loops detect high traffic in one area moving in a certain way, they can self-adjust to keep traffic flowing better. I’d think that knowing what traffic looks like 2-3 intersections in all directions would be an extremely helpful thing for letting a stoplight determine what its timing may be now, and in 5 minutes. There was a study not too long ago that showed that traffic would flow better if each traffic light dynamically adjusted the timing based on the current traffic at that light. But this was opposed to setting the timing based on the average traffic at that time of day, which is the usual mode for traffic lights. They didn’t consider having different traffic lights talk to each other. Doing that would be more difficult and I suspect not produce much better traffic flow. As for the terminology: roundabout and traffic circle refer to two different, albeit similar, things. Traffic circles are usually older constructions (dating from before the 70s roughly) while roundabouts are newer and adhere to certain design constraints. In the US, we largely stopped putting traffic circles in before the roundabout was invented and didn’t adapt to them immediately, so Americans tend to use the older term as a generic. But in more recent times, some places in the US have built modern roundabouts and that term is usually used for them locally. We don’t have very many here in the Portland area (somewhere around 2 dozen in the entire metro area) but other places have more. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [December 20, 2016, 7:37pm UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071/23 "2016-12-20T19:37:09Z")
> [@gotpasswords](#): > > There’s a fair bit of voodoo in figuring out the timing of metering lights. Let too few cars through on a cycle, or let one car through per cycle with too long between cycles, and traffic approaching the bridge, freeway or roundabout backs up. Conversely, trying to allow too much traffic through will clog the “downstream” traffic flow. > > This is one of those cases where automation hasn’t caught up to human’s innate fuzzy logic. The larger issue in most of this stuff is that the physical resources are simply inadequate. EIther slightly so or grossly so. Traffic engineering in that environment is about choosing the least bad choice from several bad-to-awful choices. All of which are flat unacceptable if driver efficiency was the sole measure of merit. Freeways here clog at rush hour. Because instead of 4-5 lanes wide each way they ought to be 15 lanes wide each way. On & off ramps clog at rush hour because instead of being 1, 2, or 3 lanes wide they should be 4, 6, or 8 lanes wide. Major surface streets clog at rush hour because instead of being 3 lanes each way plus a center left turn lane they ought to be 10 lanes each way. Traffic engineering is about doing the best possible job of cramming 10 lbs of stuff into an (at best) 5lb bag. In many cases it’s 10 lbs into a 1 lb bag. As drivers we’re stuck dealing with 2x to 10x overloaded roads & intersections. Which is not to say every signals engineer in every jurisdiction is a rocket scientist. But is to say that anyone who thinks tweaking timing can make high volume traffic disappear hasn’t actually studied the science at all. There may be a 2 or 4 or even 10% gain available if the configurable stuff is particularly dorked up at a particular junction. Expecting more is fantasy thinking. And in the 90% typical case stuff isn’t extra dorked up-it’s as good as the installed tech can make it. For awhile I lived at the edge of suburbia where new housing and new on/offramps from the freeway were being built all the time as suburbia spread like a fungus out into ruralia. In each case the state could only afford to create the cheapest smallest type of on/offramps: single lane diamonds with a pair of 4-way traffic signals 200 feet apart. ([Diamond interchange - Wikipedia](https://en.wikipedia.org/wiki/Diamond_interchange)). And they instantly became massive gridlocky clogs as the new houses filled up and every morning and evening 90% of the traffic was on one path through the two lights which required a left turn at one of them. So then 5 years later they got the money to tear out the small diamond interchange and build a more efficient type, the 2-lane (or even 3-lane in some cases) SPUI ([Single-point urban interchange - Wikipedia](https://en.wikipedia.org/wiki/Single-point_urban_interchange)). This design is able to flow about 4x the traffic for only about 2x the money. And works well on both balanced and unbalanced flows. It’s superior in every way. Long term they would have been money ahead to just build the adequate interchange first. But they were always behind the 8-ball paying for the prior mistakes which never left enough money to start doing this right. So each interchange was built wrong on purpose due to budget limitations then immediately added to the back of the queue to be replaced as fast as the money would allow. And this was in an area with unlimited low cost land to build the larger on/offramps out into. Something pretty rare in the UK or the US northeast. Bottom line: ameliorating traffic costs money. There is no guarantee the money available has any connection to the amount of amelioration required. Roundabouts only scale so much. After that you need full limited access roadways with slip ramps on and off. It seems the OP’s intersection exceeds the scaling limits. A lot of surface jamming comes from people being willing to enter an intersection before they are sure they’ll get out the other side before their side goes red and cross traffic goes green. So they end up trapped in the intersection nose to tail on their red light while cross traffic can’t move at all on their green. If I was King there’d be a large claw on a large automated crane with a car crusher installed at each intersection where this is a problem. Cars trapped in the intersection would be immediately picked up by the claw and dropped into the crusher. With all the people still aboard. That way cross traffic could use their green light for going, not for staring at the side of a gridlocked car. This kind of selfish driving is active vandalism to civilized traffic flow. And of course the more other jerky people do it, the more even reasonable non-jerky people believe they have to just to avoid being a patsy. Death to vandals. ---
**Author:** ![chrisk](https://avatars.discourse-cdn.com/v4/letter/c/6de8d8/32.png) [@chrisk](https://boards.straightdope.com/u/chrisk)\ **Post date:** [December 20, 2016, 8:26pm UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071/24 "2016-12-20T20:26:57Z")
> [@jtur88](#): > > Closer to home, an example right here in this forum. When starting a thread, you are given space for about three words to compose a title. After three words, the first words disappear from the text entry field, so typographical errors are epidemic in threads that are otherwise more carefully proofread. The title is not seen by the poster until the thread has been posted, when it is too late to repair it without the hands-on intervention of a moderator. So,obviously, the web designer of the forum board has never actually used the product he has designed. Is that intentional hyperbole? The title box isn’t exactly roomy, but if you can only fit three words in it… either you’re seeing the UI differently than I am, or you use awfully big words in your titles! I just went to see, and I was able to fit in: This is a testing title to show the amount of space 11 words, a lot of them small, but not all of them. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [December 20, 2016, 9:00pm UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071/25 "2016-12-20T21:00:33Z")
> [@chrisk](#): > > Is that intentional hyperbole? The title box isn’t exactly roomy, but if you can only fit three words in it… either you’re seeing the UI differently than I am, or you use awfully big words in your titles! I just went to see, and I was able to fit in: > > This is a testing title to show the amount of space > 11 words, a lot of them small, but not all of them. Agreed. On my machine the title box holds 30 ALLCAPS before it scrolls. Or 38 lowercase before scrolling. Do some of my titles scroll on input? Yes. Are there stupid forms designs, both paper and electronic, where the sizing is stupid for the input? Yes. Is this input box one of them? IMO no. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [December 20, 2016, 10:31pm UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071/26 "2016-12-20T22:31:30Z")
> [@bump](#): > > I think the problem really is that traffic control and engineering is probably more art than science. I mean, there are standards manuals for things like signage, etc… but I’d bet that actually modeling it would be one of those problems that sounds like it would be simple, but in practice is extraordinarly hard, as it’s not just modeling a half-million cars at once, it’s trying to realistically model driver behavior. And that’s probably not easily or accurately done on a level granular enough to work for an individual stoplight. > > I’m personally surprised that the streetlights in a city aren’t starting to be networked, so that if the cameras/inductive loops detect high traffic in one area moving in a certain way, they can self-adjust to keep traffic flowing better. I’d think that knowing what traffic looks like 2-3 intersections in all directions would be an extremely helpful thing for letting a stoplight determine what its timing may be now, and in 5 minutes. We could probably use a combination of chaos and monitoring to evolve custom light switching patterns for the junction that maximise flow of traffic . ---
**Author:** ![buddha\_david](https://avatars.discourse-cdn.com/v4/letter/b/ee7513/32.png) [@buddha\_david](https://boards.straightdope.com/u/buddha_david)\ **Post date:** [December 20, 2016, 11:24pm UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071/27 "2016-12-20T23:24:48Z")
Wherever you see a traffic engineering problem that hasn’t been fixed, 90% of the time it’s due to lack of money. The other 10% of the time, it’s due to lack of money. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [December 21, 2016, 12:14am UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071/28 "2016-12-21T00:14:46Z")
> [@Mijin](#): > > This is indeed the case IME. And I used to live in milton keynes, so I consider myself an expert. MK is all roundabouts and with roads on the American grid style. Try Basingstoke which has (from memory) some six access roundabouts with traffic lights - it can take ages to get round in the early hours when there is no other traffic at all. The best roundabout, with no lights, is undoubtedly Swindon’s Magic Roundabout. > **[Magic Roundabout (Swindon)](https://en.wikipedia.org/wiki/Magic_Roundabout_(Swindon))** > > The Magic Roundabout in Swindon, England, is a ring junction constructed in 1972 consisting of five mini-roundabouts arranged in a circle. Located near the County Ground, home of Swindon Town F.C., its name comes from the popular children's television series The Magic Roundabout. In 2009, it was voted the fourth-scariest junction in Britain. > The roundabout was constructed according to the design of Frank Blackmore, of the British Transport and Road Research Laboratory. Traffic flow around the... This is a really great (american made) video of it. [https://www.youtube.com/watch?v=6OGvj7GZSIo](https://www.youtube.com/watch?v=6OGvj7GZSIo) ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [December 21, 2016, 1:51am UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071/29 "2016-12-21T01:51:27Z")
The Magic Roundabout didn’t snag first place, which went to Spaghetti Junction, Birmingham, in this [list](http://news.bbc.co.uk/2/hi/uk_news/scotland/glasgow_and_west/8382506.stm). But having no lights definitely should be a class of its own. This prizewinning two and a half minute film of a traffic circle in Ho Chi Minh City–“The Most Dangerous” according to the editor of the website, not the filmmaker–is not only visually captivating but extraordinarily suggestive of the mathematics of natural phenomena and emergent behavior. I am not a mathematician, but the mathematics of what is now termed emergent behavior is not co-evalent with chaos theory. Swarm computation/simulation pops up all over the place. The Sante Fe Institute struck me from the beginning as having a Steve Jobs-black-t-shirt style hipness, just in time to match when “chaos-is-a-real-thing-sez-scientists” exploded in the 1980s. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [December 21, 2016, 2:17am UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071/30 "2016-12-21T02:17:49Z")
> [@Leo\_Bloom](#): > > … > This prizewinning two and a half minute film of a traffic circle in Ho Chi Minh City–“The Most Dangerous” according to the editor of the website, not the filmmaker–is not only visually captivating but extraordinarily suggestive of the mathematics of natural phenomena and emergent behavior… Whoops.[Here’s the page.](http://www.npr.org/sections/krulwich/2013/06/10/190468911/the-most-dangerous-traffic-circle-in-the-world) ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [December 21, 2016, 7:57am UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071/31 "2016-12-21T07:57:49Z")
> [@Mangetout](#): > > It made me wonder if some of these junctions would be better if there was a bit of randomness introduced in the timings - in particular, to allow the sets of lights to fall in and out of phase with one another - so the dominant flow of traffic could not completely impede the others (as happened to me yesterday). > > So… is this sort of randomness or deliberate phase drift ever used in traffic light sequencing in multi-light junctions? “Dither” is frequently introduced into control problems like this. Pseudo-random dither is rarely introduced into control problems like this. True randomness is possible bu almost never used. (Due to increasing cost and complexity for each level.) But traffic signals around here are typically controlled by very very simple controllers, which don’t have any capacity for dither of any kind. Regarding traffic lights turned off, yes, when the power goes off, the traffic lights go off, and when I was younger, that always made the traffic flow better. Now, I don’t think that’s the case. Maybe because the timing is better, or because there are more cars now, or perhaps modern drivers just aren’t used to driving through uncontrolled instersections. Regarding the increasing number of controlled intersections in the UK: my life experience leads me to believe that something like a fixed budget is available for “upgrading” intersections, and that the budget, rather than the need, controls the number of intersections that are “upgraded” each year. Unless there is complete economic collapse, eventually all intersections and pendestrian crossings will be controlled by traffic lights. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [December 21, 2016, 9:04am UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071/32 "2016-12-21T09:04:19Z")
> [@Melbourne](#): > > Regarding the increasing number of controlled intersections in the UK: my life experience leads me to believe that something like a fixed budget is available for “upgrading” intersections, and that the budget, rather than the need, controls the number of intersections that are “upgraded” each year. Unless there is complete economic collapse, eventually all intersections and pendestrian crossings will be controlled by traffic lights. We’ll just about have it done ready for when autonomous self-driving cars become mainstream, and traffic lights become completely obsolete. ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [December 21, 2016, 11:12am UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071/33 "2016-12-21T11:12:49Z")
> [@Mangetout](#): > > It made me wonder if some of these junctions would be better if there was a bit of randomness introduced in the timings yes and no. Well it might be possible to get the fixed timing right so that you don’t have this problem. But yes if the road is blocked, then you just get the situation that one road gets priority over the other. A more sensible fix for an intersection is to have the cameras ensure the round robin is at work… a few vehicles from here, a few from there. This relieves the frustration of not being able to turn or U turn, because there’s just no room until the vehicle in front moves a bit ! Some intersection clusters work very well because of the fixed/synchronation of the timings of the lights at the cluster. But you are right that varying timing (doesn’t have to be random) can help spread the flow onto different roads. BTW Chaos theory had two results 1. “a butterfly COULD change the weather”. COULD at some extremely remote change 2. You can make fancy patterns ,even repeating patterns, from what appears to be random noise. Well we know its carefully constructed algorithm that deceives that way… but still thats what fractals are … (although the engineering people had been avoiding operating harmonic systems near poles for decades ! and sort of knew that the frequencies of the system would be predictable here and unpredictable there…so "Chaos’ and “fractals” are not as new as the naming. ) ---
**Author:** ![aldiboronti](https://avatars.discourse-cdn.com/v4/letter/a/9fc348/32.png) [@aldiboronti](https://boards.straightdope.com/u/aldiboronti)\ **Post date:** [December 21, 2016, 12:39pm UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071/34 "2016-12-21T12:39:38Z")
[Here’s a reference](http://www.telegraph.co.uk/news/2016/04/29/calls-for-traffic-lights-to-be-switched-off-as-study-finds-drive/) to what I was talking about upthread, ie the removal of traffic lights improving the flow of traffic. > [@](#): > > The Dutch town of Makkinga removed all signs and other controls with success. In Ashford, Kent, traffic lights were removed in 2008 and the road layout was simplified. Accident rates fell by 41 per cent, with evidence that congestion has eased, despite a rise in the number of road users. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [December 22, 2016, 6:41am UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071/35 "2016-12-22T06:41:52Z")
> [@aldiboronti](#): > > [Here’s a reference](http://www.telegraph.co.uk/news/2016/04/29/calls-for-traffic-lights-to-be-switched-off-as-study-finds-drive/) to what I was talking about upthread, ie the removal of traffic lights improving the flow of traffic. I keep hearing about experiments and schemes like this, but they never seem to make it to mainstream, even though they are reported as being overwhelmingly successful. ---
**Author:** ![buddha\_david](https://avatars.discourse-cdn.com/v4/letter/b/ee7513/32.png) [@buddha\_david](https://boards.straightdope.com/u/buddha_david)\ **Post date:** [December 22, 2016, 1:58pm UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071/36 "2016-12-22T13:58:44Z")
> [@Mangetout](#): > > I keep hearing about experiments and schemes like this, but they never seem to make it to mainstream, even though they are reported as being overwhelmingly successful. Plus it’s always in some tiny town that probably didn’t have more than one or two stoplights to begin with. The experiment would never work in place like Los Angeles. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [December 22, 2016, 2:10pm UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071/37 "2016-12-22T14:10:32Z")
I saw a guy on TV last night who worked for TFL (Transport For London). His job was analysing traffic flow, using cameras and under-surface sensors to try and come up with better traffic light sequencing. There are conflicting requirements: They want to give busses priority to encourage use of public transport; they want to give cyclists a safer route through complicated junctions, and they want to keep the general traffic moving, so the solution is not easy. ---
**Author:** ![Channing\_Idaho\_Banks](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/channing_idaho_banks/32/250_2.png) [@Channing\_Idaho\_Banks](https://boards.straightdope.com/u/Channing_Idaho_Banks)\ **Post date:** [December 22, 2016, 3:22pm UTC](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071/38 "2016-12-22T15:22:11Z")
In San Francisco there are certain street lights that skip the red cycle periodically. You can get tricked by these because the countdown for the Pedestrian Crossing ends while the light is yellow but instead of going red it turns green again for another 20 seconds before going yellow and red again. It’s confusing, but I think they tried to add some type of random complexity to their system of off-and-on switches. [Previous page](https://boards.straightdope.com/t/do-traffic-light-sequences-ever-make-use-of-chaos-in-their-timings/775071.md?page=1)