The wave-particle duality of traffic in Beijing
Created | Updated Jun 24, 2005
Beijing, capital of China, is home to some 12 million people1 and until very recently its wide avenues were all but empty of motorised traffic. That was then - but wow, has everything changed now!
The transmission medium - roads
The avenues of Beijing are vast 6 lane monsters 2, arranged in a grid formation with the Forbidden City and Tiananmen square at its centre. At regular intervals these are intersected by 2 lane roads 3 and the area between these is filled with an indescribable mesh of minor 1 lane roads 4.
Slow moving super-heavy particle flows - Trucks
Trucks in Beijing are frequently overloaded, rarely have more that 4 gears and are fueled by very low grade petrol. The result is that they are very slow indeed. They also don't tend to have power assisted steering, so their drivers will go through life trying to make as few manouvers as possible. When a truck hits its optimum speed it is pretty sure to stay at that speed and in that lane for as long as possible - if this happens to be what we in the west might refer to as the "overtaking" lane, so be it.
Medium amplitude wave-particles - Minibusses
Minibusses in Beijing are usually driven by failed racing car drivers. However, Beijing minibusses differ from those in the rest of the world in that the damping component of their suspension is largely innefective. When the bus swings out to the left, say, the whole body will sway over to the left then spring back to the right and so on in a decreasing series of oscillations.
High energy, high amplitude wave-paticles - Taxis
Taxis would get along just fine in this system, just ambling around and getting stuck in traffic, were it not for one minor difference between Beijing taxis and the rest of the world. In Beijing the pick up charge is such a significant portion of the total cost that a taxi driver makes the most money by getting as many journeys done in as short a time as possible...which means driving very fast. Of course, the road is fairly full of lorries which won't change lane, and buses swerving around them so that in order for a taxi to go froward at any speed they need to weave around from lane to lane. The amplitude of this wave is in direct proportion to the forward velocity of the taxi.
Short lived and transient particles - bicycles and pedicabs
In amongst this fast moving are a large number of smaller objects which move more slowly and in seemingly random directions as if by Brownian motion. These are the bicycles and pedicabs5 and their slowness is due to the fact that they are not motorised at all.