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Author Topic: Why does traffic clump together?  (Read 12845 times)

Offline MartinTheK

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Why does traffic clump together?
« on: 20/05/2009 04:53:53 »
I drive at the speed limit on cruise control.

Obviously I get passed a lot, but I notice that traffic goes by in clumps. Is there some theoretical reason (maybe someting involving entropy?) for this behavior? It is clearly unsafe to exced the speed limit by bunching up like that - even in fog.
« Last Edit: 01/06/2009 20:31:26 by chris »


 

Offline Bored chemist

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Re: Why does traffic clump together?
« Reply #1 on: 20/05/2009 19:02:25 »
The soimple reason traffic gets bunched up is that it's often difficult (or ot doesn't seem worthwhile) to overtake.
 

Offline techmind

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Re: Why does traffic clump together?
« Reply #2 on: 20/05/2009 22:40:58 »
If one driver chooses to go slightly slower than the car in front then the gap simply widens, but if his preferred speed is slightly greater than the car in front he will catch up with the car in front and, if it's not practical/worthwhile/too close to the speed limit to overtake, a clump begins to form.

See the very wonderful
 http://trafficwaves.org/
for more related information on applied traffic theory.

I try to be a jam-busting, fuel-economising, calming influence when I'm on the road [8D]
« Last Edit: 20/05/2009 22:52:23 by techmind »
 

Offline Don_1

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Re: Why does traffic clump together?
« Reply #3 on: 21/05/2009 07:31:37 »
Drivers who, for reasons best known to themselves, refuse to use the nearside lane prevent faster drivers from overtaking, so you get a long line of vehicles stuck behind. This is particularly the case for trucks over 7.5 ton, which are barred from the offside lane and can't get passed some silly sod who is doing less than 55mph in the center lane.
 

lyner

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Re: Why does traffic clump together?
« Reply #4 on: 21/05/2009 16:13:59 »
D1, you're such a boy racer. Just ease up and turn on the radio. Just don't get cross.

The scary thing about these bunching waves is that the back of a queue travels backwards at a fantastic rate. The people at the back of the queue may need to apply their brakes extremely quickly to avoid piling into the guy in front. These new fangled elevated brake lights are a real godsend under those conditions. It needn't be too much of a surprise when the guy in front slows down sharply when you can see three or four cars ahead applying their brakes.
 

Offline Don_1

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Re: Why does traffic clump together?
« Reply #5 on: 21/05/2009 16:29:04 »
D1, you're such a boy racer.

BOY!!!! Crumbs, me a boy!!! Thank you. I shall print this out and show others that I am a BOY, Not a old git.
 

lyner

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Re: Why does traffic clump together?
« Reply #6 on: 21/05/2009 17:42:08 »
Boy racing is a state of mind - not chronological phenomenon, dear boy!
 

Offline rosy

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Re: Why does traffic clump together?
« Reply #7 on: 21/05/2009 18:37:19 »
Quote
Drivers who, for reasons best known to themselves, refuse to use the nearside lane prevent faster drivers from overtaking, so you get a long line of vehicles stuck behind. This is particularly the case for trucks over 7.5 ton, which are barred from the offside lane and can't get passed some silly sod who is doing less than 55mph in the center lane.
Of course, you get the same effect with the sort of twerps who think they have a god-given right to do 85 mph (that's 15 mph above the legal limit, for those not based in the UK) all the way from Cambridge to London and come roaring up behind those of us doing 68 mph whilst overtaking a lorry flashing their headlights, and who expect us to undertake a merge/remerge manoeuver to let them past even when there's barely space between two consecutive slow-moving vehicles to fit a car into.
They tend to be the same people who pull into the nearside lane for about a microsecond between two obviously consecutive overtaking manoeuvers even when there is no traffic behind them and no reason to do so. They also brake down to about 52 at the least sign of a speed enforcement camera, endangering those of us rolling along at legal speeds by suddenly coming to a virtual stop infront of us.
Amusingly, these are also typically the same people who complain about the "crippling cost" of fuel taxes... someone really should let them into the whole thing about air resistance, poor lambs.
 

Offline turnipsock

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Re: Why does traffic clump together?
« Reply #8 on: 22/05/2009 00:59:34 »
When one lorry overtakes another lorry it's like a rolling road block on the two 'slower' lanes. Its caused be various tolerances in lorry speed limiters and some lorries limited to 54mph and some to 56mph.

The net result is that all the cars have to move to the outside lane. What Rosy says is true, people do get annoyed at people sitting at 68 mph but its because there is a huge line of traffic.

It gets to the point where people start driving up the middle lane and undertaking everybody, then cutting out forcing people in the outside lane to brake, that car behind brakes a little more and then you get a domino effect that can end up in the outside lane being stationary for a second or two.

I have found the best way to combat this is to get alongside the two lorries and the match their speed, allowing the road to clear in front. When the lorry in the middle is clear just accelerate hard and move to the middle or nearside lane.

Repeat this manouver a few times and the jams will be behind you. Just don't stop for your tea or you'll come out into a huge jam.
 

Offline DoctorBeaver

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Re: Why does traffic clump together?
« Reply #9 on: 26/05/2009 12:50:52 »
Middle lane hoggers are a menace. I remember 1 particular occasion when I was driving from London to Cambridge (yes,Rosy - the M11 again!) at around 3am. There was no traffic at all and suddenly, there in front of me, was a car in the middle lane. I was doing about 75-80mph at the time (yeah, I know) and caught the car up so fast it couldn't have been doing more than 55-60mph. I had to change from the nearside lane to the outside lane & back again to get past.

But, back to the topic. What Turnipjock said is absolutely right. People pulling into the outside lane and forcing others to brake is a major cause of bunching.

Whilst I agree with Rosy's point about people driving at 85mph, I have often been forced to drive at speeds up to 90mph in the outside lane because that seems to be the average speed. I don't want to be stuck behind 60mph middle lane hoggers or lorries that take 5 miles to overtake other lorries. On more than 1 occasion I've been forced up to almost 100mph to get into the outside lane to overtake (that seems particularly the case on the M1).
 

Offline dentstudent

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Re: Why does traffic clump together?
« Reply #10 on: 26/05/2009 12:53:11 »
I was forced to do 130mph on Saturday. Ahhhh! Empty autobahns!
 

Offline DoctorBeaver

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Re: Why does traffic clump together?
« Reply #11 on: 26/05/2009 20:14:18 »
I was forced to do 130mph on Saturday. Ahhhh! Empty autobahns!

Oh I know. They're such a trial.
 

Offline turnipsock

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Re: Why does traffic clump together?
« Reply #12 on: 26/05/2009 23:27:25 »
I came up the M6/M74 on Sunday night, starting at Stratford Upon Avon at 0015.

I was thinking, while on the M6, there isn't a straight section on the M6 so I was switching from lane to lane in order to get the shortest line but I was still coming across people who just sat in the middle lane. It was one of my better ideas, switching lanes, as it stopped me falling asleep. I could also see which way the road was going to go with the satnav.

There was one point, on the M74, where I was slowing closing on a middle lane driver. I was on the inside lane and thought she would move over as I approached...but she didn't move. I made a big deal of going to the outside lane and then back to the nearside to pass her. She never moved out of the middle lane, I guess she was planing on doing the whole journey in the middle lane or something.

dent, I get a lot of wind noise from the sunroof at anything over 130mph...how do you get around that?
 

Offline MartinTheK

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Re: Why does traffic clump together?
« Reply #13 on: 27/05/2009 06:25:18 »
interesting  comments.

I have a modest proposal to alleviate the California budget deficit which is currently heading north of 20 bevabucks.

If the safe drivers were deputized as the state traffic posse comitatus and equipped with dashboard cameras AND the law was tweaked to make it illegal to  own a car exceeding the speed limit ...

Then the people speeding past them could be mined as a good source of state revenue.

On the drive home from San Francisco last weekend I could have generated $100,000 easily.
 

Offline Don_1

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Re: Why does traffic clump together?
« Reply #14 on: 27/05/2009 11:47:49 »
dent, I get a lot of wind noise from the sunroof at anything over 130mph...how do you get around that?

Might one suggest sticking to the 70mph speed limit!

..... make it illegal to  own a car exceeding the speed limit ...


Which speed limit? town, urban or motorway/autoroute/autobahn/freeway?


If the safe drivers were deputized as the state traffic posse .....

..... those who dislike them would run them off the road, shoot them and torch their car.

I think there is enough 'road rage' as it is and the US position regarding guns would make matters 100 x's worse.


Then the people speeding past them could be mined as a good source of state revenue.

On the drive home from San Francisco last weekend I could have generated $100,000 easily.

In the UK drivers are already clobbered with fines for driving, parking, farting and just about everything else.
 

Offline dentstudent

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Re: Why does traffic clump together?
« Reply #15 on: 27/05/2009 12:17:16 »
dent, I get a lot of wind noise from the sunroof at anything over 130mph...how do you get around that?

That's EASY! I don't have a sunroof...
 

Offline MartinTheK

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Re: Why does traffic clump together?
« Reply #16 on: 27/05/2009 15:38:18 »
It's already possibly worth your life to stick your tongue out at other drivers in California.

We can make the dash cams very inconspicuous and if 2 % of the cars on the road are possee members...

I don't know about UK drivers, but anybody in an SUV in California is obviously a rich class traitor who deserves to be clobbered by taxes for the common good.

NB Gas in California is currently about $2.50 when it was over $4.00 they would slow down to a slight degree. At $24.50 a gallon -- madness takes control.

How about this - scratch the posse idea. Let's issue letter's of marque band pay 5% of the fines recovered to the road privateers.

Arrrh, me hearties! Were out for gold, so we are -- even though it looks like were innocentlyyoff to the market.
 

lyner

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Re: Why does traffic clump together?
« Reply #17 on: 31/05/2009 16:39:04 »
People are obsessed with going fast!
The problem is that people CHOOSE a lifestyle which involves longer journeys than are good for them. It's a vicious circle based on peer pressure and the consumer society. I know that many people feel that they have no option but many of them, if fact, do have a choice.
If it really is as upsetting as they make it out to be, then they should consider a different choice of workplace / living place / holiday destination and reap the benefit.
I expect strong replies from a few who claim to have no choice but . . . .
 

Offline turnipsock

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Re: Why does traffic clump together?
« Reply #18 on: 31/05/2009 21:22:35 »
When I was driving back from London to Glasgow, for work, I spotted several middle lane hoggers.




Like this guy.
 

Offline dentstudent

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Re: Why does traffic clump together?
« Reply #19 on: 31/05/2009 22:09:06 »
When I was driving back from London to Glasgow, for work, I spotted several middle lane hoggers.

Clumping not too much of a problem, there though, eh? ;)
 

Offline Chemistry4me

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Re: Why does traffic clump together?
« Reply #20 on: 01/06/2009 00:57:57 »
What's wrong with hogging the middle lane? Am I being an ignorant fool here or am I missing something?
 

lyner

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Re: Why does traffic clump together?
« Reply #21 on: 01/06/2009 16:41:28 »
When I was driving back from London to Glasgow, for work, I spotted several middle lane hoggers.

Like this guy.
In fact, he'd just overtaken you whilst you were asleep!
But you had a choice of two sides to get back past him. What's to complain about?
 

Offline chris

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Why does traffic clump together?
« Reply #22 on: 01/06/2009 20:40:41 »
It really p1sses me off when people drive slowly in the middle lane. Countless times I've been snarled up in traffic on motorways and often the slow lane is half empty yet moving at the same speed as the berk driving slowly in the middle of the road. This forces everyone travelling at a half decent speed (at the speed limit even!) to have to use the fast line. All these manoeuvres slow everyone down and also trigger panic breaking with the result that there are accidents. So if some of these turkeys moved into the bloody LEFT lane occasionally (and that includes the bloody lorries) then life would be better all round.

Chris
 

Offline Chemistry4me

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Why does traffic clump together?
« Reply #23 on: 01/06/2009 21:03:37 »
Oh, you have a slow and fast lane?
 

Offline techmind

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Why does traffic clump together?
« Reply #24 on: 01/06/2009 21:38:20 »
What's wrong with hogging the middle lane? Am I being an ignorant fool here or am I missing something?
...
Oh, you have a slow and fast lane?

On main (trunk) roads and motorways where we have two or three lanes in each direction, the lane nearest the outside of the road (i.e. left hand hand) is slowest and the lane nearest the centre of the road (i.e. right hand lane) is fastest. (We drive on the left).

On a three-lane motorway, strictly the left-hand 2 lanes are for slow and faster-moving traffic while the right-hand lane is for overtaking only. In practice on a congested motorway the right-hand lane is just the fastest lane.

In UK traffic law, it is illegal to 'undertake' (ie to overtake a slower vehicle to your right). To remain legal, this means that if you're travelling in an empty 'slow' lane and come across a 'middle-lane hog' travelling slower than you, you need to pull over two lanes to pass it on the correct side. On a quiet road this is just annoying.

I did see it suggested on another forum that you could try doing circuits of overtaking the middle-lane-hog then pulling over, allowing yourself to be overtaken... and repeat to see how many times before they notice. Although it's amusing to visualise, I don't recommend it though, even on an empty road, in case it leads to a road-rage incident.

In my limited experience driving on motorways I've still found it surprising just how often 'messy' traffic situations (traffic bunching, sudden braking etc) on a busier motorway can ultimately be traced to a middle-lane hog. These people are oblivious to the chaos they're causing for everyone else!
« Last Edit: 01/06/2009 21:40:02 by techmind »
 

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Why does traffic clump together?
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