Traffic jam mystery solved by mathematicians (someone alert the Fed)

Physorg ^ | December 19, 2007 | University of Exeter

[ckilmer]

Traffic jam mystery solved by mathematicians
Mathematicians from the University of Exeter have solved the mystery of traffic jams by developing a model to show how major delays occur on our roads, with no apparent cause. Many traffic jams leave drivers baffled as they finally reach the end of a tail-back to find no visible cause for their delay.
Now, a team of mathematicians from the Universities of Exeter, Bristol and Budapest, have found the answer and published their findings in leading academic journal Proceedings of the Royal Society. The team developed a mathematical model to show the impact of unexpected events such as a lorry pulling out of its lane on a dual carriageway. Their model revealed that slowing down below a critical speed when reacting to such an event, a driver would force the car behind to slow down further and the next car back to reduce its speed further still. The result of this is that several miles back, cars would finally grind to a halt, with drivers oblivious to the reason for their delay. The model predicts that this is a very typical scenario on a busy highway (above 15 vehicles per km). The jam moves backwards through the traffic creating a so-called ‘backward travelling wave’, which drivers may encounter many miles upstream, several minutes after it was triggered. Dr Gábor Orosz of the University of Exeter said: “As many of us prepare to travel long distances to see family and friends over Christmas, we’re likely to experience the frustration of getting stuck in a traffic jam that seems to have no cause. Our model shows that overreaction of a single driver can have enormous impact on the rest of the traffic, leading to massive delays.” Drivers and policy-makers have not previously known why jams like this occur, though many have put it down to the sheer volume of traffic. While this clearly plays a part in this new theory, the main issue is around the smoothness of traffic flow. According to the model, heavy traffic will not automatically lead to congestion but can be smooth-flowing. This model takes into account the time-delay in drivers’ reactions, which lead to drivers braking more heavily than would have been necessary had they identified and reacted to a problem ahead a second earlier. Dr Orosz continued: “When you tap your brake, the traffic may come to a full stand-still several miles behind you. It really matters how hard you brake - a slight braking from a driver who has identified a problem early will allow the traffic flow to remain smooth. Heavier braking, usually caused by a driver reacting late to a problem, can affect traffic flow for many miles.” The research team now plans to develop a model for cars equipped with new electronic devices, which could cut down on over-braking as a result of slow reactions. Source: University of Exeter
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[ckilmer]

Someone needs to show the math of this to people at the fed--and they need to farm this math to mathematician/economist teams who can build this into their models. Modelling traffic as flow of a compressible fluid in a pipe was done by Honeywell Systems and Research Center (USA) in the early to mid 1970s. AFAIK, this was the first use of this paradigm; might be applicable as well to money flow models

[kalee]

ping

[decal]

“Our model shows that overreaction of a single driver can have enormous impact on the rest of the traffic, leading to massive delays.”

A better question would be: How come this twit is always in front of ME?

[rellimpank]

—it is the reverse of the situation when you see the traffic light 17 vehicles ahead of you turn green but instead of the group gently starting to move, half of the group have to wait til the one in front of them gets off the cell phone and moves-—

[steve86]

Isn't all that prima facie obvious? What on earth else would cause the backup besides someone harshly applying brakes near the front?

[dayglored]

Clearly, braking is the cause of the problem.

FEDERAL MANDATE: REMOVE ALL BRAKES FROM AUTOMOBILES.

[flowerplough]

A ‘backward travelling wave’ of prudence, caution, and delay on the dual carriageways, eh? ‘Tis indeed my good fortune to live so far out in the wild.

[eyedigress]

Their model revealed that slowing down below a critical speed when reacting to such an event, a driver would force the car behind to slow down further and the next car back to reduce its speed further still.

That is incredible, now we know.

[robomatik]

alert the media too!!!

[GOP Poet]

yep and I always behind you—LOL:)a

[Santa Fe_Conservative]

Gosh, this history major solved how traffic jams happen long ago without silly old math.

[The KG9 Kid]

I'm no civil engineer, but I'm pretty sure that I know the reason traffic seems to halt for no reason in the Los Angeles basin's freeways:

Miles ahead, there's always some joker who decides to get off at the next exit from the far left lane. They abruptly cut off two or three lanes of traffic to do it.

Miles back, traffic comes to a dead stop in just under a minute.

I've seen this firsthand when I noticed a bumbling driver cross three lanes of traffic on a slight upgrade causing all lanes of traffic to hit their brakes at the same time I had KFWB traffic radio on. Within five minutes the traffic channel was reporting stopped traffic in all lanes at the next traffic update. I thought to myself 'Well, now I know how traffic stops for no reason'.

Once that happens, impatient drivers miles back perform needless lane changes just so they can get in the lane that they perceive as still moving along. This can even cause several road rage incidents, all because of a handful of disobedient, impatient, and negligent drivers.

Boy, I'm glad I no longer live where there's high density traffic. When I lived in SoCal, I used to drive an hour and a half each way to work and back. Never again will I waste my life like that.

[dayglored]

> Isn't all that prima facie obvious? What on earth else would cause the backup besides someone harshly applying brakes near the front?

Of course. But the point of the article is that a relatively small, transient event (one person applying their brakes, and then moving back up to speed) has a growing effect backwards in traffic, until some distance behind, a lot of people are coming to a complete halt. The fact that braking causes it is secondary. The interesting observation is the multiplying effect rippling back through the traffic.

[SouthTexas]

This all began happening when they removed the “chrome horn” from the front of vehicles.

[TrueKnightGalahad]

Since I find this type of traffic jam among life’s worst frustrations, I propose that a system be installed in all new cars that incorporates a shotgun shell, aimed at the driver’s seat and triggered when the in-car electronics analyse slow reaction times and consequent over-braking. This would have three benefits: 1) the guilty driver would never again make that mistake; 2) other drivers would be much more aware of the total road situation to avoid #1, promoting much higher levels of driving skills; and 3) since the initial over-braking will have caused a traffic jam anyway, having to remove the car and formerly-corporeal driver would at least give us a REAL reason for the tie-up. :-)

[Cementjungle]

Isn't all that prima facie obvious? What on earth else would cause the backup besides someone harshly applying brakes near the front?

Well, sometimes it's the good old car chase (at least if you live in L.A.).

[Greg67]

“The research team now plans to develop a model for cars equipped with new electronic devices, which could cut down on over-braking as a result of slow reactions.”

Proposed solution is worse compared with the problem. If a pedestrian suddenly appears in my headlights how the device is going adapt?? Or has anyone seen a problem couple of cars ahead of you? A big one, and reacted before the cars in front of you.

[ThomasThomas]

I have noticed that traffic slows where carpool have an entrance / exit. When cars try to cross several lanes to get to an exit. This is one reasons why carpools doesn’t help the flow of traffic.

[VOA]

I guess it’s nice the mathematicians have built a working model.

But when I lived in Los Angeles during 1995-2005, the traffic reporters
on stations like KABC 790AM would often talk about the origin of
traffic jams thusly: At 6:30 AM, somebody hits their brakes, probably
for no reason...and by 6:35 AM, you’ve got a major jam on the same
stretch of road.

Or you’ve got “lookie-loos” that decide they’ve got to reduce speed fairly
fast by 15-20 mph in order to scope that gawd-awful wreck on the other
side of the road. Next thing you know, there’s an enforced slowdown of
their traffic lanes reaching back a mile or more.

[razorback-bert]

I saw this very explanation some years ago on a cable show.