The Census Bureau released American Community Survey estimates for 2013 last week, which report that the number of people biking to work in Chicago has decreased from 1.6 percent in 2012 to 1.4 percent in 2013. This could well prove to be a one-year blip against a broader, multi-year trend that has seen bike commuting nearly triple since 2000.
Other cities have also seen temporary declines in this key statistic, then went on to see strong gains. In New York City, the Census reported that the proportion of workers commuting by bike dropped in 2008 and 2009, but then doubled in subsequent years. Streetsblog Network's earlier story on the data release included a chart from Bike Portland showing the growth of bike commutes in various cities, with substantial year-to-year fluctuation across all of them. For instance, Portland's commute rate dipped in 2007, then rocketed by 50 percent in 2008 -- and that gain has stuck ever since.
It's easy to overstate the importance of the Census' bike-to-work statistic. This number is widely reported mostly because the reliable Census Bureau updates it annually, and makes it easy to find and compare. Ultimately, though, national advocates acknowledge that it's a woefully incomplete measure of bicycling, and not just because it only measures commute trips.
The particular dataset released last week, the American Community Survey one-year estimate for 2013, is particularly unreliable because it draws from a very small sample: The total number of Chicagoans who told the Census they biked to work last year numbers around 400. A shift of just a few dozen people, for reasons like poor weather or pure chance, can impact the final tally. Due to the small sample size, the survey has a margin of error of plus or minus 0.2 percentage points. So, the true mode share in 2013 could have gone up relative to 2012, decreased even more, or stayed the same.
The American Community Survey also reports estimates based on several years of surveys, which are more reliable but which would be even slower to pick up on rapidly changing phenomena. Bicycling in Chicago is improving quickly, and even the 2013 survey (which is administered monthly) wouldn't have captured the full impact of many miles of new protected or buffered bike lanes and a huge bike-sharing system -- both of which should meaningfully increase the number of Chicagoans biking to work.
The more reliable multi-year estimates from the American Community Survey are due later this year, and in 2015 a new National Household Travel Survey will give us a better look at bicycling for non-work trips. Chicago doesn't have to wait for the feds to tell us about what's happening on our own streets, though. The area can always do its own measures of bicycling, for instance through in-depth travel surveys (perhaps piggybacking on the NHTS, as other areas do) or through on-street counts.
Updated with a clarification about the survey's margin of error.
