The health benefits of riding a bike are obvious, and they seem to outweigh the risks of other city hazards — collisions, pollution, biased newspaper editorials, etc. Recent data models on cycling in the Netherlands and Barcelona concluded that the upside of physical activity was much larger than the combined downsides of traffic accidents and inhaling toxins. So in addition to improving a city transportation system, bike riding might elevate public health.
One way to expand urban biking is through a bike share, but since these systems are quite young in North America, there's not a great deal of evidence to show how much they increase ridership. Bike shares certainly make it easier to access a bike in the city: you no longer have to buy one, or rent an apartment big enough to fit one, or live in a building decent enough to store one. Still, giving better access to existing riders isn't the same as creating new ones.
To get a better handle on the potential public health benefits of bike-share systems, a group of Canadian researchers led by Daniel Fuller recently evaluated the ridership effects of Montreal's great program, BIXI. In the March 2013 issue [PDF] of the American Journal of Public Health, Fuller and company report that if you build it, the riders will (eventually) come:
The BIXI public bicycle share program in Montreal was associated with greater likelihood of cycling after the second season of implementation for respondents exposed to the BIXI program.
BIXI — short from BIcycle-taXI, which doesn't make a ton of sense, until you realize they probably made it want to rhyme with hockey — launched in May 2009. By 2011 it was the largest bike share in North America, with some 5,050 bikes at 405 docking stations. The program gives bike access to roughly 380,000 Montreal residents.
Fuller and company tracked rates of cycling in the city at three points in the BIXI timeline: its launch (May-June 2009), after its first season (late 2009), and after its second season (late 2010). They conducted a self-report phone survey of cycling activity (total, commute-related, and recreational) in the previous week, noting whether or not a person had ridden at least 10 minutes. All told they included about 7,000 city residents.
Once they controlled for seasonality, the researchers found that exposure to a BIXI station was associated with a significant increase in the likelihood of bike riding. The change didn't occur overnight. After the first season of BIXI there was a slight positive trend, but nothing measurable. By the end of the second season, however, Montreal residents who lived near a bike-share docking station were much more likely to be people who rode a bike.
In basic terms, implementing bike share may have shifted local behavior toward a healthier transportation alternative.
Now the caveats of causation apply here. Other factors no doubt entered into play, including media campaigns for riding, as well as expansions to the city's bike infrastructure. That said, there weren't any major infrastructure additions between the start of the bike-share program and the end of its second season. Also, the phone survey was limited to landlines, which may have reduced the number of young participants. If anything, then, the rate of cycling seems like it would be understated.
Graph from Daniel Fuller et. al. Impact Evaluation of a Public Bicycle Share Program on Cycling: A Case Example of BIXI in Montreal, Quebec. American Journal of Public Health (2013), 103(3), pp. e85-e92. doi: 10.2105/AJPH.2012.300917.