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City road networks grow like biological systems


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City road networks grow like biological systems


  • 12:51 23 April 2008
  • NewScientist.com news service
  • Belle Dumé

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 in Bruyères-le-Châtel and Alessandro Flammini 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 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)

Link:
http://technology.newscientist.com/article/dn13759-city-road-networks-grow-like-biological-systems.html

Não é incrível tudo o que pode caber dentro de um lápis?...

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