no name

Most of the world's cities started from an important marketplace or town square .
town square: 都市広場｛とし ひろば｝

Over time , they developed multiple centers where people could work , shop and play .
Over time: 規定外労働時間、時間外労働、超過勤務、残業、超過勤務手当、(試合の)延長時間、延長戦

But why ? Some economists have suggested that cities fragment because of agglomeration-businesses that spring up in clusters increase their chances of success .
fragment: 破片、断片、かけら、断章、未完遺稿、残存断片物
spring up: 躍り上がる、踊り上がる、おどり上がる、生う、跳ね上がる、ギンッ、〈はね上がる〉・飛び上がる、躍り上がる、〈飛び上がる〉・跳ね上がる、〈跳び上がる〉・跳ねる

Yet physicists have arrived at a slightly different explanation :
traffic jams .

Marc Barthelemy and R\xe9mi Louf , both at the Institute of Theoretical Physics in France , designed a mathematical model to explain how cities and their surrounding suburbs evolve .

Their research suggests that as a city grows and congested roadways make it increasingly difficult to get to the center , subcenters emerge along the outskirts .
congested: 密集した、混雑した、(…で)渋滞して、混雑して、充血した
outskirts: はずれ、郊外

It's an interplay between how attractive the place is and how much time it takes to go there , Barthelemy says .
interplay: 相互作用

Cities with accommodating transportation networks remain centralized longer , he adds .
centralized longer:

The physicists validated their ideas using data from 9,000 U.S. cities and towns of different sizes .

A better understanding of how metropolitan areas evolve could prove useful , considering that two thirds of the world's population is expected to live in urban areas by 2050, notes David Levinson , a transportation engineer at the University of Minnesota .

There's a lot of urbanization left to happen , Levinson says .
left to happen: 

If planners imagine a city to take a particular form , but that's not the way the city wants to behave , we'll be making unwise investments .

Barthelemy believes the model could also come in handy for estimating traffic delays , gas consumption and carbon dioxide emissions .
come in handy: ある目的に役立つ

I think that this opens up the path to some really quantitative insights about cities , he says .
open up: (…を)広げる、開拓する、開店する、始める、あける、開く
quantitative: 量の、量に関する、量的な

We can take simple mechanisms , simple ingredients , and in the end predict how important properties are scaling with population .
scale with: ～に対応｛たいおう｝する