While accidents, "rubber-necking" and construction work can and do also cause long delays on the road, Japanese researchers have confirmed that dreaded traffic jams often result from the most obvious cause too many cars!

Their research, published in the New Journal of Physics this week, was based on model patterns normally used to understand the movement of many-particle systems.

But when applied to an actual traffic situation, they proved that even tiny fluctuations in car-road density caused a chain reaction which could lead to a jam.

They found that very small fluctuations in speed by drivers had a cumulative effect and, once the traffic volume reached a critical density, even gentle braking rushed back over drivers like a wave and could cause a standstill.

In their experiment, the researchers put 22 cars on a 230-metre circular track and asked drivers to go at a steady 30km/h.

The initially free-flowing movement was upset by one driver altering his speed and soon concertinaed around the track, causing brief standstills.

A Nagoya University physicist said that although the emerging jam in the experiment was small, its behaviour was no 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 plan to experiment with longer road sections and more vehicles.

Cape Town can probably offer them plenty of trial sites.