http://www.physorg.com/news117283969.html

Traffic jam mystery solved by mathematicians
Car traffic
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.”



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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

 

yup, that's what i have been telling my wife all along. she always wonder how come traffic suddenly comes to stop, crawl for miles, and then go back to normal without any incident.

i told her it's caused by some people braking or slowing down, and that triggers a chain reaction back, etc... guess i was right!

 

They needed mathematicians to figure it out?

 

thats why i hate drivers who kept too much safety distance, they didn't realize the effect on the people behind them.

this is similar to the bull-whip effect i guess.

 

keeping a safety distance i think is ok, but it's all those extra braking and such when people change lanes, etc....

i also notice two spots where usually traffic jams (what's a better location than socal....) when the freeway goes up and then down, close towards the "peak" of that freeway portion, there is usually traffic. that's coz' people couldn't see what's on the other side of the peak, so they brake and slow down. another one is when the freeway turns either left or right where you can really see that far after the turn. traffic again

some of these i think are unavoidable. on my route every day i go through these types of roads and i see traffic all the time

 

i remember on Top Gear they did this during the newscast...

James May figured out it'd take a speed of about 250mph to negate any slowing down caused by a 4-lane highway merging into a 2-lane highway due to whatever reason...

 

minimizing braking will make traffic flow better, people tailgating each other in slow crawling traffic and braking constantly kills flow rates

 

I think its better to keep a distance so people wont brake as much. It's better to go a constant 20mph (less people will cut lanes because everything is constant) than 0-30-10-30-0 and so on.

 

well the types of traffic jams described above are short lived, the real PITA traffic is caused by bottlenecks. if you just open of those bottlenecks there could be so much less traffic.

 

well i said "too much" safety distance.
use holland tunnel as a example, some people inside are just taking their time in the tunnels, i have seen people keep over 10 car length behind the car in front of them, that 10 car lengths means people behind them would have to wait for the "artifically created" congestion where many cars could have squueze in.

holland tunnel i think it six lanes merged into 2, with a series of 5 intersections before entering the tunnel, which is why the chain reaction doesn't stop here, the extra space means somebody could miss the green light due to congestion around the merging area and created even more traffic.


especially here in NYC, i hope people driving on the road understands it's tough driving in NYC and if one's incompetent of driving in such rough conditions, kindly keep to the right or take the subway.
nyc has enough share of bottlenecks and hopefully people can avoid creating anymore of them.

 

In my area, they also happen when you have a low sun on the horizon ahead of you streaming in, at the first raindrop, at the first flake of snow, and, of course, at the first sign of a Crown Vic.

 

Damn rubber neckers....

 

In an ideal world, if everybody braked or accelerated at the exact same time, all our traffic delays (non accident related) would be solved. Think about this at a light. It's a chain reaction once the first car lets off the brake. It trickles back and is very inefficient.

Unfortunately, it will take technology to allow that.

 

That's what I thought after reading the article. "Residual backup" is a related term and is an easy concept.

Looking at it backwards, we'll notice that in a traffic jam when the leading car begins moving up to speed it could be 10 minutes or more by the time the car 300 cars back in the tail end even begins to move. Obviously, with each successive car, the one in front of you must begin to move first before you give it gas. That 3 second delay multiplies all the way down the line.

The drivers that cause these delays need to stay home.

 

Yeah, it's the easiest way to experience this effect. When you're at a light and you're 15 cars back, look how long it takes for you to finally go after the light turns green. It's ridiculous.