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Street layouts have a major influence on people鈥檚 decisions to drive or travel by foot, according to the first global analysis of street connectivity. The findings could be used by urban planners to design cities with lower climate impacts.

Christopher Barrington-Leigh at McGill University in Canada and Adam Millard-Ball at the University of California, Santa Cruz, assessed the connectivity of street networks in different cities by counting the numbers of intersections, streets radiating off each intersection, dead ends and loops, and measuring the straightness of the routes between each intersection. They performed this analysis on all 46 million kilometres of the world鈥檚 mapped roads.

The results show that cities with grid-like street patterns, such as Buenos Aires, Alexandria, Osaka and Taipei, have the best connectivity. Old European cities like Paris and Vienna also score well 鈥� despite their intersections tending to be irregularly spaced and three-way instead of four-way 鈥� because they still form highly connected networks.

At the other end of the spectrum, cities that favour cul-de-sacs and crescents 鈥� like Raleigh, Manchester and Bangkok 鈥� are the least well-connected because their curvy, dead-end streets create disjointed suburban islands.

Since well-connected streets make it easier to walk, cycle and access public transport, cities with greater street connectivity tend to have lower rates of car ownership and higher proportions of people walking to work.

This suggests that the way we design urban spaces now will have long-lasting impacts on the use of cars and their greenhouse gas emissions, because once streets are laid down, they are essentially 鈥渓ocked in鈥�, says Barrington-Leigh. 鈥淭he choice about street connectivity in new developments is one of the largest climate-relevant investments that humankind is making and yet it鈥檚 been grossly overlooked,鈥� he says.

In the US, prioritising street connectivity in new developments would reduce car emissions in 2050 by 9 per cent, says Barrington-Leigh. The impacts are likely to be even bigger in places like China and India, where entire cities are being constructed from scratch, he says. Overall, the amount of urban space across the world is set to triple between 2000 and 2030.

Good street connectivity may also lower climate emissions because it makes it easier for people to come together and share resources, says Barrington-Leigh. 鈥淚n contrast, if you live in cul-de-sac hell in the suburbs, it鈥檚 harder to get anywhere, so you might have a swimming pool in your backyard instead of going to the local public pool, or a home theatre in your basement instead of going to the cinema, or a large freezer because you can鈥檛 go shopping as often,鈥� he says.

Historically, street grids were idealised in Ancient Rome and China because they facilitated efficient transport of people and goods. Cul-de-sacs became popular in the US and UK in the 20th century when cars made it possible for people to spread out and planners thought they would create safe havens for kids to 鈥減lay street hockey or run over to their neighbours鈥欌��, says Barrington-Leigh. However, research shows that people are actually than on grid-like streets, possibly because they are less cautious and the curvy roads make them less visible to drivers.