When I was in Helsinki a couple of summers ago, I came across an incredibly simple and appealing innovation: a human highway for pedestrians and cyclists.

Snaking through the city core, the Baana — or "fast lane" — is a converted railway track. On foot or bicycle, I could safely and easily access many key points in Helsinki without breathing in exhaust from cars or worrying about getting crushed under a truck. And if I so desired, I could even stop for a basketball or table tennis game at designated outdoor courts along the way.





The Baana was constructed in 2012, part of a revival of bicycle-friendly infrastructure in the Finnish capital. Other European capitals — Amsterdam, Copenhagen — have long been pictures of cycling perfection, and major cities around the world, from Rabat to Bogota, have been making pushes to build up bike lanes and low-cost bike rental systems as a means of improving public health and reducing air pollution.

During my week in Helsinki, I used a bike much more than I did in my then-hometown Toronto, a city that's incredibly hostile to cyclists, where you often feel you're putting your life in your hands every time you hop on for a ride. It was a win for both my health and the environment.

How a city is designed can matter as much for health as diet or medical care

Recently, doctors have been calling on policymakers to make other cities more like Helsinki (or Copenhagen, or Amsterdam), where the urban infrastructure is conducive to "active transport" — which just means walking and cycling to get around.

Similarly, in June The Lancet medical journal published a landmark report on why the medical community needs to galvanize against climate change, what it called "the greatest global health opportunity of the 21st century." One idea here is that changing our built environment doesn't just reduce greenhouse gas emissions — it can also make us healthier.

What these calls all have in common is a reorientation of how we think of health. We often think about health as something personal: It depends on what we choose to eat, what medicines we take, and whether we drink or smoke.

But long before those individual decisions, the environments we live in can play a huge role in shaping our health — and this is especially true when it comes to the design of our cities.

How to design a healthier city

The way cities are set up can determine whether we feel compelled to use a car or bus to get to work, instead of our legs or a bike. Opting for the latter, the public health argument goes, is hugely beneficial on a variety of fronts. There's good evidence that cities designed to be walkable and bike-friendly carry both health and environmental benefits. Researchers in Barcelona, for example, recently measured the risks and benefits of the city's bike-sharing scheme, Bicing. They found that it got more people cycling, and reduced carbon dioxide emissions in the city.

As a recent Lancet report summed up: "Active travel (walking and cycling) can reduce the risk of ischaemic heart disease, obesity, diabetes, some types of cancer, and all-cause mortality, while also averting costs to health systems and reducing greenhouse gas emissions."

Fifty percent of the world’s population now lives in cities and that's only going to increase — something the World Bank's Timothy Bouley, a health and climate specialist, sees as a huge global health opportunity. "If you build cities the right way — with bike lanes, clean energy, the right kinds of bus and rapid transport systems, buildings with stairs instead of elevators — you can really encourage healthy habits in people."

So bike lanes are just one way to improve public health and reduce emissions. A less visible way to make cities greener is by retrofitting buildings, said Andy Haines, a professor at the London School of Hygiene & Tropical Medicine who studies the health co-benefits of the low-carbon economy. If you make old buildings more efficient by insulating them and improving their ventilation systems, they use less energy, and the people inside of them are exposed to cleaner air. In pollution-heavy Beijing, buildings like the Parkview Green Hotel are popping up that promise not only low energy usage but also more breathable air.

Building out green spaces in cities is another way to improve public health. "Some studies show improvements in health and mental health related to green spaces," Haines explained. "Green spaces can also help to protect against urban heat island, or the potential for cities to warm up more than the surrounding countryside in hot weather."

But he also noted that a precondition for using green spaces is whether people feel safe in them. If you live in a neighborhood marred by gang violence, for example, you're probably not going to hang out in your local park. And maybe you're not going to go for a jog or bike to work, even with the best sidewalks and bike lanes in place. In other words, improving the environment for health means a lot more than just designing greener cities, but at least it's a start.