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Old 12-18-2016, 01:42 PM
Mangetout Mangetout is offline
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Do traffic light sequences ever make use of chaos in their timings?

I was stuck in traffic yesterday (at this junction right here) - it's a roundabout that has 4 streams of traffic entering it and there are lights controlling some of the streams (that is switching between traffic going around the roundabout vs traffic entering it).

It's a common setup - and the precise details of this junction are not important (except to say that this is not just like a four way intersection - it's different because traffic typically has to traverse more than one set of lights at different parts of the junction.. What happened yesterday is that for a couple of the roads entering the junction, traffic was backed up solid and hardly moving at all, because the lights were essentially working against each other - so traffic was either streaming through too fast to enter, or filling up the junction when the lights turned red.

Every time the lights went green (so technically, my lane would be able to go), we had to give way to a stream of traffic that was being allowed into the junction. Every time that flow was stopped, the space we had to drive into was choked with stationary cars.

Now, I know that studies are done on these junctions and traffic flow is modelled - I think in many cases, the lights are programmed to work in pattern that is the least worst compromise, and some junctions have patterns that are different at different hours of the day, or dependent on sensors (these seemed to be very strictly sequenced though).

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?
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Old 12-19-2016, 11:26 AM
Me_Billy Me_Billy is offline
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The trend in traffic engineering is to use sensors to detect traffic and adjust the lights accordingly.

Note that previously only sensors embedded in the road could do this, but now cameras mounted above the road can detect vehicles - much cheaper!

So the thing to do is install sensors there. Also traffic engineers MAY NOT KNOW about the problem if no one tells them! Have you called them to report the problem?
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Old 12-19-2016, 11:45 AM
jz78817 jz78817 is offline
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doesn't placing signals at the entrances kind of defeat the purpose of a roundabout?
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Old 12-19-2016, 12:04 PM
bob++ bob++ is offline
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Originally Posted by jz78817 View Post
doesn't placing signals at the entrances kind of defeat the purpose of a roundabout?
On this particular roundabout, like many others, the main traffic stream is all in the same direction (The A3 in this case), which gives traffic entering from the minor road (Church St) no chance to slip in. The traffic lights are there to allow this, but traffic can be so heavy that it makes little difference.

I know Portsmouth fairly well and it is an overcrowded city built on an island. It is a major ferry, freight and naval port, all of which add to the traffic in this area.

Traffic lights on roundabouts work well at peak times, but in my opinion they should be turned off when traffic is low.

Last edited by bob++; 12-19-2016 at 12:05 PM.
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Old 12-19-2016, 12:08 PM
BeepKillBeep BeepKillBeep is offline
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Somewhat related, what I'm often wondered is if traffic engineers assume that drivers will be obeying the law or not.

For example, there shouldn't be any cars in an intersection (I know the OP is talking about a roundabout but their OP is what made me think of this) after the light turns red because they shouldn't be there. You're only supposed to proceed with your turn when you are clear to complete. Of course, very few people do this. Similarly, speed limits generally mean less than 10 over the posted speed limit.

So when doing their calculations do they use the cultural norms or the law?

Last edited by BeepKillBeep; 12-19-2016 at 12:13 PM.
  #6  
Old 12-19-2016, 12:24 PM
Channing Idaho Banks Channing Idaho Banks is offline
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I run into the scenario all the time. You wait and wait and wait and wait for your turn to go, the light turns green, and the whole Road is filled up with cars you can't even cross the intersection.

In this scenario, you might even be tempted to run a red light since this might be your only chance to actually get through the intersection. Even if there was a cop nearby he couldn't get you cuz of the so much traffic.
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Old 12-19-2016, 01:36 PM
Mangetout Mangetout is offline
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Originally Posted by jz78817 View Post
doesn't placing signals at the entrances kind of defeat the purpose of a roundabout?
Yes - roundabouts were originally conceived to be self-regulating systems, however, nearly all busy roundabouts in the UK now have traffic lights added to them, to try to regulate the flow of traffic.
I guess in some cases, the absence of lights would mean that traffic entering from some junctions would just never get a chance to enter the flow of traffic, but as someone who has seen traffic lights go from rarity to ubiquity, it does seem wrong to me. There are many cases of light systems near me that are so designed that they only permit one or two cars through certain routes on each cycle.
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Old 12-19-2016, 01:38 PM
Mangetout Mangetout is offline
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I run into the scenario all the time. You wait and wait and wait and wait for your turn to go, the light turns green, and the whole Road is filled up with cars you can't even cross the intersection.
Exactly so - and I reckon if the lights were allowed to drift out of phase, there would be cycles when this didn't happen to you (of course the opposing traffic streams would be inconvenienced, but perhaps only by an amount that balances the permitted flow from your lane - and so it should be acceptable.
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Old 12-19-2016, 02:06 PM
gotpasswords gotpasswords is offline
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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.
  #10  
Old 12-19-2016, 04:42 PM
hibernicus hibernicus is online now
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Originally Posted by jz78817 View Post
doesn't placing signals at the entrances kind of defeat the purpose of a roundabout?
Yes, it does. I think the correct approach when a roundabout doesn't work (because of mismatched traffic flows on different inbound routes) is to remove the roundabout and replace it with a signalled junction.

(I realise this is one of those subjects - like grammar - where everyone has an opinion, informed or otherwise. If a traffic engineer tells me I'm wrong about this, I'll happily defer.)
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Old 12-19-2016, 07:15 PM
Mdcastle Mdcastle is offline
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Originally Posted by BeepKillBeep View Post
Somewhat related, what I'm often wondered is if traffic engineers assume that drivers will be obeying the law or not.

For example, there shouldn't be any cars in an intersection (I know the OP is talking about a roundabout but their OP is what made me think of this) after the light turns red because they shouldn't be there. You're only supposed to proceed with your turn when you are clear to complete. Of course, very few people do this. Similarly, speed limits generally mean less than 10 over the posted speed limit.

So when doing their calculations do they use the cultural norms or the law?
Engineers are very pragmatic. If there's a problem they'll try to fix it rather than ignoring it because they followed the instruction manual while designing it so it's OK, suggesting drivers have it coming if they're so stupid, or suggesting the city get some cops patrolling out there.

Pulling into the intersection and waiting if you cannot proceed is the correct way to make a left turn. The additional time it takes to enter an intersection can mean that there's simply never a gap long enough. Having a short all-red phase is to allow any traffic legally caught in the intersection to clear it. Of course that doesn't stop those in the intersection from panicking and maybe making a rash move.

The Yellow Trap was pretty notorious (fixed by the Flashing Yellow Arrow) result of this. If the opposite direction was about to show a lagging green arrow, a driver would see the through yellow and panic and make a rash move thinking side traffic was about to be released when it is not. The flashing yellow arrow gives you the option that was previously unavailable of showing a permissive turn with a straight stop.

There's also the option of extending a flashing yellow arrow for a few seconds after the main phase ends to give stuck traffic a chance to clear without freaking them out with a red, but this is not usually used because of the impact to operations.

Last edited by Mdcastle; 12-19-2016 at 07:15 PM.
  #12  
Old 12-19-2016, 07:19 PM
BeepKillBeep BeepKillBeep is offline
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Pulling into the intersection and waiting if you cannot proceed is the correct way to make a left turn.
Huh. I just looked it up. My driver instructor was either wrong or I'm remembering what he taught me wrong.

Ignorance fought.
  #13  
Old 12-20-2016, 03:23 AM
Mangetout Mangetout is offline
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Originally Posted by hibernicus View Post
Yes, it does. I think the correct approach when a roundabout doesn't work (because of mismatched traffic flows on different inbound routes) is to remove the roundabout and replace it with a signalled junction.

(I realise this is one of those subjects - like grammar - where everyone has an opinion, informed or otherwise. If a traffic engineer tells me I'm wrong about this, I'll happily defer.)
I think you're probably right. Fitting a few sets of lights to an existing roundabout is a cheap and quick workaround, compared to redesigning the whole thing, then digging it up and rebuilding it AND adding lights.

In truth though, as soon as a roundabout has a set of lights on it, it stops being a roundabout and becomes a junction that just happens to have a circular feature in it.
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Old 12-20-2016, 05:40 AM
Mijin Mijin is offline
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Originally Posted by bob++ View Post
Traffic lights on roundabouts work well at peak times, but in my opinion they should be turned off when traffic is low.
This is indeed the case IME. And I used to live in milton keynes, so I consider myself an expert.
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Old 12-20-2016, 10:48 AM
jtur88 jtur88 is offline
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I've often wondered if traffic engineers even have a drivers license, or if it's all theoretical and "should work". When driving, one encounters many situations in which one wonders of the designers of roads (or even cars, for that mater) have ever actually driven an automobile.

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.

Last edited by jtur88; 12-20-2016 at 10:51 AM.
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Old 12-20-2016, 11:19 AM
bump bump is offline
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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.
  #17  
Old 12-20-2016, 11:30 AM
jz78817 jz78817 is offline
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Originally Posted by bump View Post
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.
most places I'm familiar with are fairly good about keeping up on traffic studies and optimizing light timings. usually when someone complains about the competence of planners and engineers, it's just out of frustration when they have to sit at a light longer than they think they should.
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Old 12-20-2016, 11:38 AM
Leo Bloom Leo Bloom is offline
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Mangetout you're a Brit? Or do they say roundabout in USA too? I (a non-driver) always thought we say traffic circle.


ETA: Linguistic forensics on speaker: I think, courtesy of some hijack, you're the snow-pea guy, not as I thought the guy-who-eats-everything guy. Only Brits and Frenchies say mange-tout for snow peas. Ergo,...

Last edited by Leo Bloom; 12-20-2016 at 11:41 AM.
  #19  
Old 12-20-2016, 11:46 AM
kenobi 65 kenobi 65 is offline
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Mangetout you're a Brit? Or do they say roundabout in USA too? I (a non-driver) always thought we say traffic circle.
It depends on where you live in the U.S. Roundabout, traffic circle, and rotary are all terms that are used in different regions of the U.S. for it.

Map showing what people in different areas call it: http://i.dailymail.co.uk/i/pix/2013/...54_634x450.jpg

Last edited by kenobi 65; 12-20-2016 at 11:47 AM.
  #20  
Old 12-20-2016, 11:53 AM
aldiboronti aldiboronti is online now
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Can't find it now but I'm sure there was a study once in the UK where they removed traffic lights from certain junctions or roundabouts and traffic flow actually improved. The uncontrolled traffic was regulating itself in a far better fashion than the lights.

I'll try to dig up a cite.
  #21  
Old 12-20-2016, 12:27 PM
jz78817 jz78817 is offline
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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://www.google.com/maps/@42.5543.../data=!3m1!1e3
  #22  
Old 12-20-2016, 01:33 PM
dtilque dtilque is online now
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Originally Posted by jtur88 View Post
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.

Quote:
Originally Posted by bump View Post
.
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.
  #23  
Old 12-20-2016, 01:37 PM
LSLGuy LSLGuy is offline
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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. (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 (https://en.wikipedia.org/wiki/Single...an_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.

Last edited by LSLGuy; 12-20-2016 at 01:40 PM.
  #24  
Old 12-20-2016, 02:26 PM
chrisk chrisk is online now
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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.
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Old 12-20-2016, 03:00 PM
LSLGuy LSLGuy is offline
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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.

Last edited by LSLGuy; 12-20-2016 at 03:01 PM.
  #26  
Old 12-20-2016, 04:31 PM
Mangetout Mangetout is offline
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Originally Posted by bump View Post
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 .
  #27  
Old 12-20-2016, 05:24 PM
buddha_david buddha_david is offline
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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.
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Old 12-20-2016, 06:14 PM
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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.

https://en.wikipedia.org/wiki/Magic_Roundabout_(Swindon)

This is a really great (american made) video of it. https://www.youtube.com/watch?v=6OGvj7GZSIo
  #29  
Old 12-20-2016, 07:51 PM
Leo Bloom Leo Bloom is offline
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The Magic Roundabout didn't snag first place, which went to Spaghetti Junction, Birmingham, in this list. 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.
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Old 12-20-2016, 08:17 PM
Leo Bloom Leo Bloom is offline
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Originally Posted by Leo Bloom View Post
...
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.
  #31  
Old 12-21-2016, 01:57 AM
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Originally Posted by Mangetout View Post
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.
  #32  
Old 12-21-2016, 03:04 AM
Mangetout Mangetout is offline
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Quote:
Originally Posted by Melbourne View Post
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.
  #33  
Old 12-21-2016, 05:12 AM
Isilder Isilder is offline
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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. )
  #34  
Old 12-21-2016, 06:39 AM
aldiboronti aldiboronti is online now
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Here's a reference to what I was talking about upthread, ie the removal of traffic lights improving the flow of traffic.

Quote:
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.
  #35  
Old 12-22-2016, 12:41 AM
Mangetout Mangetout is offline
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Originally Posted by aldiboronti View Post
Here's a reference 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.
  #36  
Old 12-22-2016, 07:58 AM
buddha_david buddha_david is offline
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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.
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Old 12-22-2016, 08:10 AM
bob++ bob++ is offline
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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.
  #38  
Old 12-22-2016, 09:22 AM
Channing Idaho Banks Channing Idaho Banks is offline
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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.
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