Solving traffic jams with maths A Swiss traffic management and transport economics expert believes a combination of queue management and computing can help solve the gridlock that plagues the modern city. Dr Dirk Helbing of ETH Zurich, a professor of sociology specializing in modeling and simulation, says “self organizing” traffic control systems, using …
> they had those black rubber bars across the road
The black rubber tubes are actually a census point. They are connected to a box chained to a pole somewhere close, and are used for gathering information about road use for planning purposes - they can determine class of vehicle, speed, wheelbase, etc.
But you're right that VA junctions are old news - only the sensors are predominantly buried into the road.
Vic.
The temporary rubber tubes placed on the surface and hooked up to a recorder are indeed census points, but I don't think that's what the post referred to. Before the buried inductive loop system was used, traffic lights were controlled by pneumatic sensors. These were metal tubes with rubber tops, buried in the road just before the lights. As a car arrived at the lights it would signal the local controller, which could then trigger a change.
I've no idea if they survived the transition to centralized computer control, or if that had inductive sensors from the beginning.
A fascinating plunge into traffic sensors!
These days, the primary detection method is inductive loops. A long time ago, rubber bars with a hose in, a more permenant version of the sensus point, were popular.
These days, more advanced sensors are getting common, for instance radar sensors that can monitor multiple lanes without having to replace on resurface. Also infra red sensors for more accurate vehical profiling, height etc.
Another recent inovation are little wireless capsules, containing an electronic compas, that detect car type/speed/count based on the vehicals disruption of the earths magnetic field. The highways agency trialed them a couple years ago, and found them much faster than loops to fit, but battery life in field remains to be proven.
Another exotic technology is multi microphone sensors which use traffic noise to give a car, lane position, speed etc. Less accurate than loops but cheaper.
The UK uses automatic traffic control in cities. The individual lights all report back to a central computer which optimises traffic flow in quite a deterministic way.
It is much cheaper to link the lights to a central station because you can just use BT phone lines.
Of course, you could do self organising by linking the lights via a central hub at the same cost, but if you do that, you lose the redundancy anyway, so there doesn't seem much point.
IMHO, real progress could be made by harnessing data from peoples GPS devices to let you know where they were trying to go. Perhaps you could send instructions back to the GPS, routing people evenly accross varius possible routes. If this happens, it will come from the GPS/mapping industry, not the traffic lights people.
"The UK uses automatic traffic control in cities. The individual lights all report back to a central computer which optimises traffic flow in quite a deterministic way."
...unless a politician determines that the traffic flow will be slower than a donkey with three gout-ridden legs and a wooden pegleg, of course.
Remember the day the Congestion Charge came in? Now compare it to how it is currently.
See?
I had a right go at TfL for a junction near Hyde Park Corner (Brompton Rd/South Ken Rd) recently - the three sets of lights there are out of sync and you can only get two cars through at a time.
The response I got is that they are actively managed and its working perfectly.
So apparently it is intentional .. ??!!
> it is intentional
Yes.
When the traffic industry says "managed", don't take that to mean "does something I consider useful".
Traffic management is about affecting driver behaviour. The actual intent might be different to what you or I would consider sane. That intent might or might not actually do some good somewhere.
Vic.
The sensors always controlled the light as well as collecting data. People used to reverse over them to make the lights change green.
Many in Australia don't use phone lines. They have a tiny solar panel for power and a wireless internet connection to the central control. Cameras monitor major roads & intersections. Human beings can change the lights for miles around, to push traffic around trouble spots.
> Using sensors to measure variables like the amount of traffic already in
> a road section, how quickly it is moving, and how long to the next change
> of lights, Dr Helbing’s approach is designed to respond to unexpected events.
Traffic systems have been doing that for decades.
If you look at an approach to a set of lights, there will generally be two sensors embedded in the road - either a diamond or a rhombus shape, depending on which manufacturer put them in. There may also be IR sensors on top of the signal heads.
Each junction has its own local controller, and is also networked to all the others in the area.
I've not been near the traffic industry for about 15 years, but all this was established technology when I was doing it...
Vic.
Get the minimum timings wrong and they can still go pear-shaped. My village has two sets of lights networked together. In the ground are the diamond-sensors, and what looks like IR cameras on top of at least one of the sets of lights.
The first set of lights controls the direction of traffic over a single-lane bridge - no room for two lanes of traffic, so it's uni-directional. About 50m after the bridge is the central-village T-junction traffic lights. The problem is that folks coming over the bridge cannot see if there is space for them to cross, so if traffic is backed up at the T-junction, then the queue to get through that can back up onto the bridge so that no-one can leave town. Unfortunately, one cycle of that means that nothing moves to leave town, so the lights assume nothing is trying to leave town (probably thinking everyone is parked, rather than queuing), so then fix that light to red - therefore no-one can leave town and the queue backs up on this reasonably busy route to elsewhere. The only way out of this scenario is for someone to run the red light over the bridge which is rather unsafe as they won't know if someone is coming at them at high speed (have seen the occasional good spirited soul get out of their car further back in the queue, run up to the bridge to stop traffic coming in to let some traffic out safely over the red so that there can be movement over the sensors to reset the system). This situation happens reliably at around 7.25am Mon-Fri, despite emails to my local controller.
Another flaw is that the induction sensors are sometimes not sensitive to pick up a bicycle and the "camera" sensors occasionally even miss a motorbike meaning two-wheel users end up stuck at the lights until eventually a car pulls up behind them (and, yes, when cycling I *DO* stop at red lights, ok?!)
Living in Watford, as I do, it's occurred to me that a set of traffic lights at four or five main entrances, to stop too much traffic in the town centre, then all the other lights could be removed, and all the other junctions turned into mini roundabouts, and there'd basically be no jams nor congestion..
The fuel savings alone would be massive.
Not all towns are the same, but this one is, the rule being "Let the traffic out as quick as you can, and stop it coming in until there's a free ride."
I'm surprised no-one's tried it.
Watford is an interesting place. The main loop around the centre has some interesting queuing. Late at night all the approach roads to the central loop (which is really a huge roundabout going all the way around the main shopping centre) are red and the loop itself is green. When you approach the traffic lights coming on, they switch to green if no traffic is coming the other way, let you onto the main loop, then you can drive around as far as you want, usually with greens all the way. As traffic gets busier, the main loop changes mode. All the entrance move to green in order, letting traffic on one stop to queue up, then letting the entire ring make progress. You normally have to stop once waiting to get on the loop, once again waiting for the loop to move, then often get most of the way around the loop in a single move. As traffic gets busier still, the control of traffic getting onto the loop tries to keep the jams out of the loop and keep the loop moving. In general it worked very well for the year that I lived there.
How do I fix bushey arches.
The same as I fix Vicarage Road. (Stop everyone at the harvester roundabout, and let them queue all the way back up towards Croxley green tube. Queues on downward sloped hills use less fuel, people just lift their foot off the brake. And then build a mini roundabout out at the end of the croxley park to let people out of the town via the back of it, towards Ricky past Camelot.)
Bushey arches is the same. The whole congestion thing is caused by the one way system round Mothercare/B&Q. If there were no lights at all there, and only a light on the dual carriage way down from the motorway, one stopping traffic by Cost Co (already there,) and one stopping people at the bottom of bushey hill from getting past the nine hole course, and lastly one stopping them coming in on that road from harrow. Then hey presto. No traffic.
Like the motorway junction on the M1 (J28 Northbound I think.) You just stop people entering the system.
Watford has full on dual carriageway all round it. A single trafiic light at the Dome Roundabout ,watford side, stops all incoming, and a small chiswick type flyover to let the cars queue by Hunton bridge and at M1 J5 instead of by asda. Hey presto.
As for traffic on the way out. Dig down onto the foot path at hunton bridge and another filter flyover to allow out.
No more than ten traffic lights. All it takes is a set of speed cameras to measure traffic density.
I always thought that the main issue at BA could be alleviated by taking out the lights at the Saab showroom and putting in a crash barrier (maybe 30 yards long or so) separating the two lanes heading towards Century park
People in the right lane opposite the Saab showroom, and coming from BA past the Mercedes showroom would be able to flow more easily, hopefully making BA itself less congested.
It's occurred to others too and works very well around Maastricht.
Most times lights are controlled by traffic sensors. During rush hour times and other periods of heavy traffic, the peripheral lights hold traffic back and some roads have unidirectional lights installed purely for flow control activated.
All the technology needed exists, including sensors and computers and a bit of software.
Sadly all that happens in most cases is that it moves an already marginal system with little contingency in case anything happens, even closer to the absolute maximum, thereby reducing the available contingency even further.
And when the supervisory system fails (as it inevitably will), the result is extended gridlock.
Nothing new here, they already knew this back in the days of The Italian Job (the proper one).
Sure, VA signals have been around for decades, and many of those systems count vehicle throughput. The back end of those systems however is a legacy of their age, so they don't pass around a lot of information and the network is often partitioned into small groups of sites with pre-determined coordination settings. My experience with signal control systems is limited though and I'd be surprised if there aren't more advanced systems outside my experience already in use.
I'm interested in the statement "For example, the system would detect that traffic on one section of road is slowing down or has stopped, and divert it to alternate routes to prevent the backfill causing gridlock." Are they suggesting that the system dynamically and forcibly changes drivers' route choices? How do you do that? The seppos aren't going to like that one.
Well, normally, I would just jack up the OSPF cost, but that doesn't work with the current automobile-traffic systems. No idea how the current lights would enforce that a path was unusable, so there would have to be other technology applied for that bit.
Sigh...as if taxes aren't high enough.
I see lots of comments about "traffic lights have been doing that for ages" - yes, but only locally. What this guy is proposing is a city-wide model, hence the huge amounts of maths involved, which is not driven by clock variations as most sensing lights are, but by actually, city-wide need (I would caveat that one, no idea if sensors can pick up bicycles etc).
He seems to have worked out the maths for a city-sized green wave which may actually work. I know of some green waves in Belgium (Hasselt) which only are green as long as you break the locally imposed speed limit, no doubt to generate revenue through the traffic cameras which append to be installed at every single light. Zürich is also a place that loves speed cameras (typically mounted in places where you should have your eyes on the road instead of on your speed, especially in 30 km/h zones), but it is a good place to try this out. First of all, the peak hour mess around Bellevue makes it easy to measure effect (just measure queue length along the lakeside), and they already have all the required sensors and controls in place.
London is another good example, with the added benefit that it is large enough to just take a section and try it. Anything that improves the West End and around Hyde Park corner (to name but two of many, many bottlenecks) is worth the money IMHO..
Another good mess to sort out is the so-called "ring of steel" around Amsterdam - the main reason people use the totally overloaded trains there is because using a car to get in from outside during peak hours is even worse..
"I would caveat that one, no idea if sensors can pick up bicycles etc"
I'm sure some can. Most, however, cannot even pick up a motorcycle. I would know, the number of times I've been stuck at a red light for an extended (i.e. abnormal, much longer than I have ever waited in a car) period of time, to have the lights change a few seconds after a car pulls up behind me.
I now avoid such junctions on the bike when I know about them.
There are some that can pick up bikes. Back in my student days I used to cycle past a car park and regularly made a slight detour to set off the car park entrance sensor and get a ticket.
I was wondering how many times I could do it before the computers would think the car park was full of cars that never chose to leave.
I use a car park with a weekly ticket.
Sometimes there's a bug in the system, so they leave the exist gate open for everyone to go out without presenting their ticket.
Then next time it won't let you in because it thinks you're still in there. You have to take a single-use ticket to be allowed in, then waste 15 mins at the office getting a credit for it.
Regarding sensors picking up (motor)bikes, I recently saw a do-it-yourself article on one of the "maker" sites that simply involves taping a couple of neodymium magnets to the frame or pedals. I don't cycle in urban areas (too scared), and so haven't tried it, but it may be worth trying.
On the "green wave", Sheffield has the exact opposite (red wave?). Getting from Hillsborough to J34 M1 (or the other way) on the main road/new ring road, travelling at the speed limit in quiet traffic, will have you stopped at over 3/4 of the lights. At night, the lights will change to red as you approach them. The only way to avoid being stuck at otherwise empty junctions is to exceed the speed limit by about 8mph - which most people do, obviously.
> taping a couple of neodymium magnets to the frame or pedals.
I wouldn't bother with that.
The sensor loop is a parallel tuned circuit - you've got a big coil of wire in the road, and a capacitor across it. The whole is driven by an oscillator - you've got a high-Q filter, so when in tune, there is negligible current flowing.
When something metal passes over the loop, the circuit loses tune, so current starts flowing. This is a very sensitive detector.
Over time, the components and road environment age, and you'll get some drift in the tuning. I did read about an idea to allow the loop driver to auto-tune, but I've no idea if that ever made it into production - it's a long time since I've done anything in this field.
Vic.
Swindon's "Northern Orbital" road has the same problem - as you enter this long stretch of 40mph dual carriageway with at least 10 junctions of traffic lights, if you're in a pack you're quite likely to hit greens but the second you hit a red you will continue to get them unless you speed. The problem is that the red opens a gap which the neighbouring lights take to mean "hey, I can go red now", which will then happen as you approach. That's why everyone does 50-60 down that stretch.
Now they're talking about using funky speed cameras that trigger the lights to go red if someone is approaching at greater than the speed limit - fun all round as you'll be damned if you do, and damned if you don't.
> What this guy is proposing is a city-wide model
Existing traffic systems have been using a city-wide model for decades.
He *might* have come up with a clever new algorithm. He probably hasn't - most such "innvoations" have a fundamental flaw that has been overcome many times[1]. But what he has *not* done is to create something entirely new - a city-wide, flow-modelled control system with feedback loops of varying sizes is in existence in most major cities around the world, and has been for a very long time.
Vic.
[1] My favourite is the single signal head: every year, some educator uses his influence to get in front of the bods at one of the big traffic companies to show off his latest protege's idea. This idea will inevitably be a signal head with a single lens, and a multi-coloured illuminator behind it. This used to be separate bulbs and a bit of optics, now it's assuredly LED. He will go through all the supposed benefits of simplified maintenance etc. Eventually, one of the audience will crack, and utter that fateful observation "red-green colour blind"...
There was an interesting case a while ago in Bangor, North Wales. The council re-modelled the junction outside the railway station. Afterwards, there were terrible traffic queues.
A few months later, the traffic lights failed and the queues disappeared. The locals all asked for the traffic lights to be removed. In typical council fashion, they ignored the local's request and fixed the traffic lights.
Many years ago, Bristol City Council spent a load of money doing studies and re-designing the Three Lamps junction leading out of Bristol on the A4 because it was a notorious bottle-neck.
Apparently the contractors they hired chucked down some temporary lights whilst they were working and the junction had never flowed more freely!
They told the Council who said "stick with our design" and, when they'd finished, it was as much of a bottle-neck as ever...!
Yeah, but then nobody ever accused Bristol CC of actually having a clue or wanting to get anything useful done. Or, for that matter, accused Bristol voters of being able to elect anything other than a bunch of chocolate hammers.
I suspect the Bristol planners go on to get jobs in the surrounding councils too - witness the nice new(ish) traffic lights installed on the A4174 by South Gloucestershire that'll cheerfully turn red as you approach them at 1a.m. with nothing else in sight. I think it's so you've got time to read the signs they've put up explaining how the traffic management (sic) is reducing emissions and improving traffic flow (it doesn't; peak time queues are worse since they were installed...)
Indeed. The tailback across the junction that means that when the other lights turn green no-one can get across.
Now if only the affected junction could then set off signs further back down the affected routes so that those with a bit of local knowledge could take a different route rather than blithely driving down the road only to be brought to stop by the sight of a line of red brake lights disappearing into the distance.
The problem here is that the inventor assumes that the city in question actually wants to do something about the traffic. My experience has been that revenue generating things like red light cameras ( which catch those go are tired of waiting ) are preferred by city managers over anything that looks like it might actually make the streets safer or more efficient.
Just within the surrounding cities I've seen light timings changed to unexpected values to cause people to break the law, and highways built with purposeful blind areas to allow cops to hide.
I predict that we will hear about this again.. In 10 years by someone else with little experience dealin with governments.
Just within the surrounding cities I've seen light timings changed to unexpected values to cause idiots who think they are above the law or who don't watch where they are going to break the law
There, fixed it for you.
Although I will agree that road planner seem to spend more money trying to generate revenue than making an efficient transport network. They also seem to try to cause you to stop as often as possible, wasting fuel and generating more revenue for the exchequer.
> nice habit of turning red on the main road, to allow side traffic to join
You want to try living in France.
Some parts of the road network still use the "priorite a droite" law, which means that slow traffic joining from minor roads has right of way over traffic already on the main road.
Other parts of the road network do not use this rule.
Vic.
Is legally the default rule on evey road in France, unless there is a sign indicating otherwise. You mostly find it in villages, as a way of slowing down the traffic on a main road going through the village. The possibility that someone could legitimately drive out of a side road in front of you is a very effective way of getting people to slow down.
It does have an unusual side effect in that anyone turning left off a main road (i.e. across traffic) must give way to an oncoming car that is turning right into the same side road, since at the point where the left-turner is half-way through the manoeuvre the other vehicle is on its right.
Main roads outside towns/villages generally have priority signs, with Yield signs on the joining side roads, to override the default.
Is to switch them off overnight (the value of 'night' being locally determined). In the US, they mostly go to 'flashing yellow', which turns the junction into that brilliant American* invention the 4-way stop. Anyone who's driven across a town at 4am will know what I mean - waiting for minutes at each (or, at least, half of) completely empty junction.
* Apologies if someone else got there first.
In South Africa they have this as well (and have done since forever)
Red Flashing = Stop
Yellow Flashing = Caution - but you have right of way (the other lights will be red flashing; treat more like a main road crossing a minor road)
And of course lots of 4 (and 5) way Stops instead of round abouts.
For those who have not come across this wonderfull invention it works like this
You MUST stop at the Stop Sign.
The 1st car to stop has right of way,
Then the 2nd car - regardless of which road it is on
Then the third.. and so on until the junction is empty (which happens surprisingly quickley)
The other Southern/Sub Shaharan African invention is to ignore trafic lights at night or if you feel unsafe; or just don't want to bother....
In Canada we have the same system, blinking red = full stop and yield right of way / blinking yellow = caution - intersection w. potential crossing traffic. Here in Germany if you have a blinking yellow light you have to give way to traffic on the road you intend to cross - no forced stop. The drivers on the right of way have no idea that a crossing is ahead as there is no signal at all to warn them of a potential hazard. I find the CDN/RSA system much safer and reassuring.
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So because a few pieces of technology don't quite fit the muster we must add loads more sensors, computers, and other pieces of electronics to control traffic. Why not step back for a second and think about the processing power in the vehicle. Yep, the drivers' brain. A lot better at working out how to cross a road than dumb computers. Will you have speeders racing through junctions? Probably, but they do so already. By removing signs and lights and other indicators drivers will have to think and they naturally slow down and cross a junction carefully.
There was an interview I read some years ago, probably linked through The Register, with an English boffin--Freeman Dyson, apparently. He had worked with a mathematician who was asked to study London traffic. The man's conclusion was that there was a minimum acceptable speed, and that whenever improvements were made, more cars would arrive to bring the average speed back down again. See http://en.wikipedia.org/wiki/Smeed%27s_law
You will remember fondly the project to create a traffic light management system we did...
It was an iterative project where successive years in turn undertook the three modules, which were something like sensor management, traffic management, traffic visualisation.
Each year the best two solutions to the module in question got merged into the main project and byt he time I did it in 2001 it was pretty good.
So this isnt new, its probably more likely that no council could find budget for it
Which was ironic in Southampton, a city with such bad traffic management that even the police jump the red lights at night out of frustration (think basingstoke but with traffic lights not roundabouts)
> Southampton, a city with such bad traffic management
Much of the traffic industry sees Southampton's management as *good*.
Quite a bit of the industry is around Soutrhampton/Fareham, so we get trials...
But the Bitterne Road junction is world-famous - traffic engineers around the globe know of it, even if they don't know which country Bitterne is in. Shame the whole design[1] went pear-shaped the minute they deregulated the buses...
Vic.
[1] The plan was to stop people buying the cheaper housing on the East side of the river, then driving in and out of the city every day,. So there is a complex set of junctions between Athelstan Road/Bullar Road and Bursledon Road that make driving private cars harder if you venture off the main road, but prioritises buses (top bit of Bitterne Road, Garfield Road). The idea was to make public transport *much* more viable than private. And then they deregulated the buses, so it isn't.
I lived in Tulsa, Oklahoma in the 60's and was always fascinated by the odd little metal bumps in the street placed somewhat before traffic lights. These were there to control traffic and seemed to do a rather good job of it. Major arteries would simply stay more of less green until it was indicated that a vehicle was ready to cross. I imagine that the lights were also set for various times of day also. Never could figure out why this did not seem to be in general use in other cities......
In West Germany in the v early 60's they had it solved; in many towns, inductive sensors measured traffic flow, a box with transistors (or valves?) did the maths and a speed indicator on each lamp post told you the speed to do to hit the next light at green. Ok, it might have been only 20, but it was green all the way. Peace, calm, with no smoking tyres or brakes.
"Is legally the default rule on every road in France, unless there is a sign indicating otherwise."
Many French and almost all Parisians, ignore the signs which indicate otherwise..especially on the entrances to roundabouts.. and in true French tradition treat you to the "bras d'honneur" ( little old lady drivers use this one too ) if you who are already on the roundabout and have the right of way have the temerity to sound your horn or flash your lights at them when they cut you up as they pull across you from the entrance road..
They also are incapable of driving in their own lane whether on or off a roundabout, they straddle the white lines in the middle and then move back to their own side ( grudgingly ) if something is coming the other way..We even have a TV ad for an insurance company ACM which shows an animation of a road viewed through the car windscreen , with the white lines in the middle of the windscreen coming towards the car..impossible unless the car is straddling the lines..But as nearly all French ( including police and Gendarmes ) drive like this, right down the middle of the road ..they think that this is how "normal" driving looks!
France only counts road deaths as such ,if the death of the person occurs within 3 days of a road accident..if they die on the fourth or subsequent day after being involved in a road traffic accident ( as a pedestrian , cyclist , driver , whatever ) their death is not included in road traffic accident statistics..Even so the death rate due to RTA is about the 3rd highest In Europe, and they're leaving out most of those who are counted in other countries..
In over 20 years here I've never seen anyone stopped for using a phone whilst driving, but the police or Gendarmes do wait on roundabouts to see who is not wearing a seat belt..or just to check ID papers..
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