December 26, 2007


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. (Physorg, 12/19/07)

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.

On the bright side, people in cars deserve to be stuck.

Posted by Orrin Judd at December 26, 2007 12:02 AM

Took a team ... a team ... of mathematicians to figure that out, eh?

Posted by: ghostcat at December 26, 2007 12:46 AM

No doubt the "mathematicians" are women drivers.

Posted by: Brian at December 26, 2007 4:05 AM

Serious comment from an experienced driver who is neither a traffic engineer nor a mathematician: the wave effect described above seems related to following too closely. If drivers are keeping proper interval, the taffic stream should have enough compressibility to allow for minor adjusments without producing the wave of stopped cars.

Posted by: Lou Gots at December 26, 2007 5:09 AM

Soon cars will carry mandatory devices that impose such distancing. Y'all will threaten to drive '68 Buicks instead....

Posted by: oj at December 26, 2007 8:26 AM

Actually, far from chugging along, Amtrak is late, system-wide, 30% of the time and 60% of the time on long-distance routes.

Posted by: Ibid at December 26, 2007 9:40 AM

Don't forget that passenger trains disrupt the flow of traffic on railroads because the cattle inside get restless at the slightest delay. Something that doesn't happen to wheat or lumber or autoparts or coal or containers from China.

God created railroads to carry freight, which is why Amtrak is the tool of Satan.

Posted by: Raoul Ortega at December 26, 2007 11:15 AM

Right on Raoul!

oj, my father-in-law had a pre-war (WW2) 12 cylinder Buick that bested a fire hydrant when my husband had his first driving lesson. Next best thing to a Hummer. I'd love to drive that car again – gas prices be d*mned.

Posted by: erp at December 26, 2007 12:54 PM

A '68 Buick Grand Sport? I'd live in traffic if I could have one of those.
Shoot, I could think of above five models from the '68 Buck line alone that I'd give a major organ to posses.

Posted by: Bryan at December 26, 2007 1:32 PM

I don't know what this article was going on about; my undergrad applied math degree included nearly a week on that nearly 20 years ago.

Posted by: Mike Earl at December 26, 2007 3:56 PM