Is biking in cities good for you?

Monday, December 30, 2013

This post originally appeared on The Sieve.

Life presents us all with certain problems, one of them being how to move ourselves from place to place. I submit that if you live in a compact, congested city, there’s really only one sane solution: ride a bicycle. Biking is carbon-neutral, it’s efficient, it’s outdoors, it’s exercise, it’s free, it’s fun. It’s a win-win-win-win-win-win.

But as I’m dodging morning traffic on my way to work in Washington, DC, I do find myself wondering, am I just crazy? Could the health benefits from bike commuting possibly outweigh the risk of getting flattened by some latte-swilling, texting SUV driver? And even if I avoid that fate, what about the longer-term effects of the exhaust fumes I’m sucking in with every breath?

Morning traffic into DC
Morning traffic on my ride into DC.

Since I am a science writer, I feel compelled to try to answer such questions with data. So it was troubling to find that one of the few sources providing data on the risks of different modes of transport puts biking near the top in deaths per journeys, miles traveled, or time spent in transit (apparently based on a 15-year old British survey). Only motorcycling, which is essentially bicycling at the speed of car traffic, proved more dangerous. U.S. data from a similar time period and cited in this paper tell a similar story.

While these statistics are sobering, I realize their relevance to me is unclear. For one thing, they may not reflect the recent upsurge in biking, which has started to make the activity safer in some places (more on this later). But more to the point, they don’t answer the question I really need answered, which is what is my personal level of risk, at my level of biking competence, when I ride along my typical routes?

Data to answer that question are starting to become available. Dave Love, a public health researcher at Johns Hopkins University, told me about a study in which he and his colleagues biked around Baltimore with cameras affixed to their helmets, and collected data on how close cars came to them. When Love and his colleagues were riding in bike lanes, cars maintained the minimum three-foot passing distance generally considered safe. On roads without bike lanes, however, cars often came closer than three feet when passing. Based on plenty of personal experience, I am not surprised.

Bike lanes are a good start, but bikers are even safer on cycle tracks or paths completely separated from roads, says Greg Billing, advocacy coordinator for the Washington Area Bicyclist Association. Fully separated bike networks are common in European cities like Amsterdam, where the cycling rate is much higher and crashes are relatively rare. Separated bike facilities are just catching on here; the cycle tracks on DC’s 15th and L Streets, for example, are great, as far as they go. But for most U.S. bike commuters, including me, a fully protected ride to work is not yet an option.

Bike researchers and advocates also talk about safety in numbers: the idea that one cyclist in a sea of car traffic is far more vulnerable than a school of cyclists pedaling together. Indeed, one of the benefits of cycle tracks is that they concentrate bikers along certain routes. Three to four hundred bikers per hour ride on DC’s 15th Street cycle track during rush hour, says Billing; nearby streets see far less bike traffic. Beyond the safety issue, I have also found that having a dedicated space is an empowering experience; for once I feel like I, as a biker, actually belong here, and am not just riding on someone else’s road.

A protected bike lane in New York City. (from Wikimedia Commons)
A protected bike lane in New York City. From Wikimedia Commons.

The benefits of bike infrastructure are just starting to show up in city-wide statistics in the U.S. In Minneapolis, which Bicycling Magazine has ranked as the top biking city in the country, the number of reported crashes has remained steady even as ridership roughly doubled. Portland, Oregon, another top biking city, has seen a similar decrease in the crash rate, though the total number of accidents is still increasing. Billing says that as of the last time DC released crash data, for the year 2011, the city didn’t quite have the ridership to bend the curve on the crash rate. But it’s getting close: the fraction of the city’s residents who commute by bike increased from 1.16% to 4.1% from 2005 to 2012.

Air pollution exposure, the effects of which accrue gradually, presents a totally different kind of health risk from accidents, which either cause injury or death or don’t. But the same measures that have been shown to bring down the crash rate can also protect bikers from toxic car exhaust or pollution resulting from brake and tire wear. For instance, bikers separated from cars by even a few feet will inhale far fewer toxic particles, says Audrey de Nazelle, an environmental health researcher at Imperial College London. Researchers in London found that the number of fine particulates in the air decreases substantially even between the side of a sidewalk closest to the road and the far side. And even if you don’t have access to a bike lane or cycle track, that’s no reason to get in your car, de Nazelle adds: most studies have found that the amount of pollution in the air surrounding drivers sitting in traffic is greater than that on the side of the road where bikers ride, though cyclists may inhale more pollution because they are breathing harder.

De Nazelle and others are now starting to do studies that get at the question I’m trying to answer. They have run computer models that compute how accident and disease rates would change in various cities if a certain fraction of the population switched from driving to biking. Researchers who ran such studies run in London, Barcelona and the Netherlands found that the health benefits bicyclists gain from doing aerobic exercise, in terms of reduced heart disease, stroke and so on, overwhelm any increase in accident- and pollution-related risks (see table 1 of this review paper). Unfortunately, similar results for U.S. cities so far seem to be lacking.

The gold standard for assessing health risks and benefits is a long-term longitudinal study, which follows a large group of people for long enough to see lifestyle choices reflected in disease and death statistics. Such research has been key in establishing, for example, that exercise reduces the risk of heart disease, and smoking increases it. But these studies are expensive and difficult to run, and are therefore rare, and the few that have been run have not looked at bicycling specifically, Love says. So for the foreseeable future, studies like de Nazelle’s, which project established risk and benefit factors onto specific behaviors like biking, may be what we have to go with.

I asked the researchers I spoke with whether they have changed their biking decisions based on what they’ve learned; they said they had. Love says he tries to avoid riding at night and in bad weather, when crash rates are higher. De Nazelle has changed her route choice to prioritize safety over efficiency. “I used to always choose the quickest routes; now I choose routes that I think will have fewer cars,” she says. De Nazelle also frequently bikes with her child, and she notes that her risk calculation changed when she had a passenger’s safety as well as her own to consider.

So, armed with data and expert opinion, I return to my original question—am I insane to bike right down a major DC commuting artery with no bike lane? I think the answer is, it’s complicated. On the one hand, I assume certain avoidable risks by placing my unprotected self in proximity to large, polluting fast-moving metal boxes controlled by people of varying competence and sanity. (And before I get accused of being anti-driver, I should confess that I also own and drive a car—sometimes *gulp* even down the same congested road I bike to work on).

On the other hand, by biking I efficiently solve not one but two problems—transportation and exercise—in a way that minimizes the environmental impact of both. I can partly reduce risk by riding defensively, wearing a helmet, and being aware of the places where accidents are most likely to occur—namely intersections. Possibly I could decrease my risk further by riding on less busy streets. But because the area where I live and ride–Prince George’s County and northeast DC–is underserved in terms of bike infrastructure relative to the rest of the region, any route that would keep me off busy roads would also add substantial time to my commute. And it can be hard to afford that time.

That’s my rationalization, but I have to admit I am also driven partly by stubborn idealism. I like to believe that if I assert my right to ride on city streets, others may be inspired to do the same. And if city planners see enough of us ditching our cars for bikes, they will eventually pay attention and build us a bike lane or cycle track, as the DC Department of Transportation long-term plan seems to imply. The more cities encourage biking and keep bikers safe, the cleaner, safer and more livable the urban environment becomes for all of us. Sometimes creating the future you want to live in means taking a bit of risk in the present.

What about you? What factors play into your decision to bike (or not bike) on certain streets?

This article was amended to reflect the fact that cyclists may inhale more air pollution than drivers because of their faster breathing rates. Most studies have found that the amount of pollution in the air surrounding drivers sitting in traffic is greater than that on the side of the road where bikers ride.


  1. Great post, Gabe! I must confess, I’m too scared to bike on the street in Atlanta. Probably because I’ve seen too many victims of road traffic accidents, working in the hospital… We desperately need a system of protected bike lanes in US cities. Atlanta has 1, but we need many more. Phil

    1. Gabe says:

      Phil, thanks for sharing your perspective as a doctor. Gina Kolata in the NY Times wrote an interesting article in which several doctors reflected the point you make: the emotional impact of seeing a crash victim – or worse, being one yourself – trumps any data-driven argument.

  2. New study– The risk of a crash or near-crash among novice drivers increased with the performance of many secondary tasks, including texting and dialing cell phones.