I have often noticed how in London the effects of traffic management
are often to cut the connections between major primary routes and the
rest of the street grid. An obvious case is the raised sections of the
Marylebone Road, however even on the ground level sections the cross
routes are generally disconnected, either physically or by one way and
turning restrictions. The consequence is that these routes are
optimised for fast through traffic, but when an accident or a
breakdown does happen you are completely stuck with no way of getting
out of the resulting jam. As a cynic I have always suspected that
this is because when these routes were 'traffic planned' in the 60's
and 70's the engineer's models could only cope with a fairly limited
number of nodes and links. It was only really feasible to run the
model if you eliminated all the routes through the surrounding urban
area. Then of course you have to build the model... the result, a less
resilient system.
Alan Penn
On 25 Sep 2008, at 03:58, Hoon Park wrote:
> Dear all Some of you may be interested in the following paper:
> 'Price of anarchy in transportation network: efficiency and
> optimality control' (http://link.aps.org/abstract/PRL/v101/e128701)
> by H Youn, M T Gastner, H Jeong, in Physical Review Letters. The
> paper was also introduced in the recent issue of Economist (13 Sep).
> The authors demonstrate, based on an analysis of travel times or
> delay in road networks of Boston, London, Newyork, that the rational
> decisions made by uncoordinated individuals to choose the quickest
> paths do not always achieve the social optimum. A proper method to
> reduce such social inefficiency, they suggest, is to modify the
> underlying road network structure. Interestingly, according to their
> simulation, it is often the most carefully installed streets to
> reduce travel times that are responsible for the worsening of
> traffic conditions; so it may be better to close them and encourage
> detours for the benefit of the society as a whole! Any comments?
> Best wishes Hoon Park
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