May is National Bike Month, and today is Bike To Work Day. It’s a pretty big event here in D.C.: Last year, over 11,000 people participated, and turnout is likely to be even higher this year (aided in part by the rapid expansion of a bikeshare program). Do these promotional events actually convince more people to ditch their cars and farecards?

According to a 2009 study, yes. The authors reviewed survey data from six U.S. cities and found that, as you might expect, physical factors play an important role in determining the rate of bicycle use. Overall, communities that sprawl don’t encourage transportation (as opposed to recreational) biking: “Greater distances mean fewer miles.” But social factors matter too. It turns out that people not only want to be reassured that bicycling is safe—they may also want to be convinced that it’s normal. The surveys consistently showed that in communities where residents viewed bicycling for transportation as normal adult behavior, ridership was higher. That makes sense: After seeing thousands of your peers pedaling into work, it’s hard to feel awkward about lugging your own bike, helmet, and mild odor into the office.