The argument that embracing a low-carbon future is a road map to economic ruin is bunk, say a band of economists who argue that investing in more efficient transportation, buildings and waste management could save cities worldwide at least $17 trillion. One way to unlock that savings is to promote bikes and buses.

The savings come from stimulating economic activity, decreasing health care costs, reducing poverty, and cutting the costs associated with urban sprawl, like time and productivity lost to traffic congestion. That's according to a report, Accelerating Low‐Carbon Development in the World’s Cities, released today by New Climate Economy, a group of economists formed to examine the costs and benefits of addressing climate change.

"For too long, there's been the same old argument used to prevent bold action on climate change, which is there's some sort of tradeoff between economic prosperity and climate action," says Nick Godfrey, an author of the report and the organization's head of policy and urban development. "In cities, that is a false choice. Actually, there is a significant confluence between promoting economic growth and prosperity, and climate action."

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Transportation comprises as much as one-third of the emission reductions the report says cities can "unlock." That's good for 3.7 gigatons of carbon reductions, which is up to 20 percent of the CO2 emissions needed to keep the global mean temperature from increasing by more more 2 degrees Celsius by the end of the century. In other words, changing how we get around could save money, and maybe the environment.

But changing how people move through a city isn't easy. More mass transit is great, but time consuming and expensive to build. Cities in the developing world will account for 90 percent of urbanization in the coming decades, and many of them will be strapped for cash. That's why the report emphasizes two particularly cost-effective modes of transportation: cycling and buses.

There are "compelling economic, social and environmental reasons for cities to invest in safe and well‐connected cycling infrastructure," the report says. Biking eases congestion, reduces health care costs, and cuts air pollution. It's an "equitable transport mode," since it's far cheaper to own and maintain a bike than a car.

And there are proven ways to promote pedaling any city can implement. Provide bike lanes, and connect them. Lower speed limits and increase penalties for drivers who hit cyclists. Distribute maps of bike paths. Start a bike sharing system—something more than 700 cities have already done.

There are great examples to follow: Paris is investing in cycling by doubling its network of bike lanes to 870 miles, creating 10,000 secure bike parking spaces, and offering financial incentives for those buying electric and conventional bikes. London and Munich want to build cycling highways, to make long commutes by bike convenient and safe. That kind of "cycle super highway" can deliver a 19 percent annual return on investment, according to the report.

Bus rapid transit (BRT) is a hybrid between traditional bus service and a subway. The buses usually get dedicated lanes, so they don't get tied up in traffic. They make infrequent stops to cover long distances quickly. Fares can be paid before boarding, to keep the vehicle moving as much as possible. The report cites a study that found a BRT system costs about $10 million per mile to establish, one tenth the price of a metro rail system.

More than 200 cities have BRT systems, Godfrey says. Lagos, Nigeria has used bus rapid transit to serve its rapidly growing population, and saved money by bringing existing bus fleets into the system—instead of spending money on a whole new pile of vehicles. New York City is using more express buses to expand public transit as well, since building new subway lines in the crammed city is almost prohibitively expensive and outrageously slow.

"There's a significant economic dividend to investing in better transit systems," Godfrey says. The key is for city leaders to consider things like cycling infrastructure and bus rapid transit not a burden, but an opportunity.