An accident? Construction work? A bottleneck? No, just too much traffic

March 4, 2008

A new study from a Japanese research group explains why we’re occasionally caught in traffic jams for no visible reason. The real origin of traffic jams often has nothing to do with obvious obstructions such as accidents or construction work but is simply the result of there being too many cars on the road.

The research, published today, Tuesday, 4 March, in the New Journal of Physics, shows how model patterns, normally used to understand the movement of many-particle systems, have been applied to real-life moving traffic. The research shows that even tiny fluctuations in car-road density cause a chain reaction which can lead to a jam.

The research found that tiny fluctuations in speed, always existing when drivers want to keep appropriate headway space, have a cumulative effect. Once traffic reaches a critical density, the cumulative effect of gentle braking rushes back over drivers like a wave and leads to a standstill.

The researchers in Japan used a circular track with a circumference of 230m. They put 22 cars on the road and asked the drivers to go steadily at 30km/h around the track. While the flow was initially free, the effect of a driver altering his speed reverberated around the track and led to brief standstills.

Yuki Sugiyama, physicist from Nagoya University, said, “Although the emerging jam in our experiment is small, its behaviour is not different from large ones on highways. When a large number of vehicles, beyond the road capacity, are successively injected into the road, the density exceeds the critical value and the free flow state becomes unstable.”

The researchers will be advancing their research by using larger roads and more vehicles to further test their findings.

The research suggests that it might be possible to estimate critical density of roads, making it possible to build roads fit for the number of drivers needing use of it or, on for example toll roads, only allowing the right number of cars access to the road to stop mid-flow traffic jams.

Source: Institute of Physics

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4 / 5 (1) Mar 04, 2008
Why would it not make a difference that they are experimenting on a circular track while we drive on long stretches of straight road?

Also, one can look at an accident causing increased traffic in the same way as the researchers: Say we build a highway with 4 lanes which is adequate to handle the traffic in the area in which it is built, but then an accident happens and two of the lanes are closed off, the proportion of cars to road space changes.

Mar 04, 2008
This comment has been removed by a moderator.
not rated yet Mar 05, 2008
Traffic is a real killer, its one of the most stressful experiences for me to drive a car!

It really pisses me off how much time is wasted in the traffic, especially when its due to ignorance and lack of foresight of other drivers, traffic jams, unsynchronized red lights and terrible road design and conditions where I live.
not rated yet Jun 06, 2009
Yeah, sperhuman, you are right all all counts. Take Melbourne, Australia for example, the antiquated trams ride on tracks built in the same lane of motor vehicles. By laws, when the tram stops for passengers getting on and off, the cars must stop behind it and wait. Add to their slow speeds, frequent stops, and tram-train crossings, where the train and trams cross them with walking pace to avoid derailing...throw in 2 trams and 2 train crossing at rush hour at the same time, and you get get the unholy mess 5 city block long!

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