I found an interesting article today (pasted below) stating that
Japanese scientists discovered on an actual circular track that cars
may slow down and the effect would move in the direction that traffic
is coming from simply from drivers varying their speeds. Of course
this is exactly what is demonstrated in the simple Traffic Basic model
that's part of the Netlogo Model Library. Hurray for Netlogo!
http://www.physorg.com/printnews.php?newsid=123831950
An accident? Construction work? A bottleneck? No, just too much traffic
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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