[Urbanstudy] City road networks grow like biological systems

[ESGINDIA]

This is an interesting article I found on New Scientist.  When roads are 
increasingly being treated as infrastructure for motor vehicles, 
hopefully such perceptions will help alter our planners and engineers 
views and make them work in more humane ways and treat these urban 
"rivers of life".

Leo


  City road networks grow like biological systems

http://www.newscientist.com/article/dn13759-city-road-networks-grow-like-biological-systems.html?full=true&print=true

    * 12:51 23 April 2008 by *Belle Dumé*
      <http://www.newscientist.com/search?rbauthors=Belle+Dum%C3%A9>
    * For similar stories, visit the *Cars and Motoring*
      <http://www.newscientist.com/topic/motoring-tech> Topic Guide

New models of city road network growth (top) create networks similar to 
those in reality (middle) and grow in similar ways to biological 
transport networks (bottom) 
<http://www.newscientist.com/data/images/ns/cms/dn13759/dn13759-1_250.jpg>

New models of city road network growth (top) create networks similar to 
those in reality (middle) and grow in similar ways to biological 
transport networks (bottom)

Next time you are lost in an unfamiliar city, console yourself with the 
knowledge that the layout of its roads are probably much the same as in 
any other.

French and US physicists have shown that the road networks in cities 
evolve driven by a simple universal mechanism despite significant 
cultural and historical differences. The resulting patterns are much 
like the veins of a leaf.

Marc Barthélemy of the French Atomic Energy Commission 
<http://www.cea.fr/english_portal/cea/identity> in Bruyères-le-Châtel 
and Alessandro Flammini 
<http://www.informatics.indiana.edu/people/profiles.asp?u=aflammin> of 
Indiana University, US, analysed street pattern data from roughly 300 
cities, including Brasilia, Cairo, Los Angeles, London, New Delhi, and 
Venice.

They found that cities' road patterns have a lot in common 
mathematically, as well as looking similar to the eye.


      'Not just planning'

The researchers developed a simple mathematical model that can recreate 
the characteristic leaf-like patterns that develop, growing a road 
network from scratch as it would in reality.

The main influence on the simulated network as it grows is the need to 
efficiently connect new areas to the existing road network - a process 
they call "local optimisation". They say the road patterns in cities 
evolve thanks to similar local efforts, as people try to connect houses, 
businesses and other infrastructures to existing roads.

Evolution has ensured that local efficiency also drives the growth of 
transport networks in biology - for example, in plant leaf veins and 
circulatory systems.

"Cities are not just the result of rational planning - in the same way 
that living organisms are not simply what is in their genetic code," 
Barthélemy told *New Scientist*.


      Growth predictions

"Beyond the economic, demographic and geographic "forces" that shape a 
town, there are a myriad of small "accidents" that contribute" he says. 
"Although these are unpredictable, they can be understood in terms of 
statistics and simple modelling."

The team's model also reveals that roads often bend, even in the absence 
of geographical obstacles, and that road intersections are generally 
perpendicular.

The study's results might be important for understanding urban growth 
and "sprawl" says Barthélemy. More than half the world's population 
lives in cities, a proportion that continues to increase.

"The approach could even help city planners to better predict how some 
street networks will evolve and to plan accordingly," he adds.

Previous models of urban development assumed that efficient transport 
across the entire network motivated the system's growth - as if planned 
from the top down. Focussing instead on the structure of local 
connections seems truer to real life, says Flammini.


      Ancient roots

"Our study provides a first step in understanding and integrating such 
networks when modelling urban growth," explains Flammini.

The researchers will now study how road networks developed over time in 
old cities, such as London and Paris. They hope to unearth other 
possible universal features that might be present to refine their model.

Despite the simplifications of the model, its results agree well with 
data from real city road networks, says complex systems specialist 
Jukka-Pekka Onnela <http://www.physics.ox.ac.uk/users/Onnela/> of Oxford 
University, UK.

Using the local efficiency of connections to drive road network growth 
looks to be a truer fit with reality than using the total cost of 
travelling across the network, says Onnela. "Especially given that the 
time scale of city growth (possibly thousands of years) and the time 
scale of urban planning (perhaps tens of years) are so clearly different."

Journal reference: /Phys. Rev. Lett./ (DOI: 
10.1103/PhysRevLett.100.138702) 
<http://dx.doi.org/10.1103/PhysRevLett.100.138702>

/*Cars and Motoring* - Learn more about the latest technologies in our 
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<http://technology.newscientist.com/channel/tech/motoring-tech>/.


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