The pattern of streets can give a clue as to the age of the area. Tightly-knit winding alleyways in European cities often date back to mediaeval times, whilst in the UK the rigid rows of brick terraces were put in place by the Victorians to house factory workers. Meanwhile, garden cities emerged during the early 20th century, with developments following an "organic" form that has curving streets branching off each other, ultimately terminating in a dead-end. So how does this layout affect the way we live?

Chris Barrington-Leigh from McGill University in Canada and Adam Millard-Ball from the University of California Santa Cruz, US, modelled the connectivity of different street layouts in North America and estimated the associated vehicle greenhouse-gas emissions. Cities such as Atlanta, which is surrounded by miles and miles of cul-de-sac-style suburbs, epitomize low connectivity, whilst San Francisco, with its highly connected tight-knit historic streets, lies at the other end of the extreme.

The more connected a neighbourhood is, the fewer miles residents tend to drive, the model revealed. Partly this is because the distances that people need to travel in a highly connected neighbourhood are shorter, but other feedback mechanisms are also at work.

"Low-connectivity streets lead to segregation of land uses, so that schools, shops, leisure facilities and jobs are likely to be further from people's homes," said Barrington-Leigh. "Low connectivity also makes the introduction of public transit impractical. These factors reinforce a dependence on cars."

The study, which is published in Environmental Research Letters (ERL), showed that for every 10% increase in neighbourhood connectivity, car ownership decreases 1.5%.

In the US, the "cul-de-sac nightmare" peaked around 1994. Since then there has been a trend back towards more connected developments, with grid patterns again finding favour. If this connectivity trend continues, Barrington-Leigh and Millard-Ball estimate that street arrangement alone will cause vehicle travel emissions to fall by around 3% by 2050. And if town planners decide to embrace connectivity even more, reductions of nearly 9% could be achieved over the same time period.

Retrofitting a cul-de-sac neighbourhood to increase connectivity is nigh on impossible. But for sprawling grid neighbourhoods like downtown Los Angeles and Vancouver there is some good news.

"Major highways that slice through neighbourhoods can be removed, and large housing plots can be subdivided," said Barrington-Leigh. The biggest gains, however, will come from ensuring that developments are designed with connectivity in mind. "The way we design new developments has major long-term consequences, as once the streets are in place the greenhouse emissions are locked in for decades to come," Barrington-Leigh added.

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