The American Community Survey’s annual estimate of the percentage of Bostonians who habitually bike to work in Boston is 1.4 percent for 2010, a 33 percent decrease from 2009’s figure of 2.1 percent.  

Boston’s bike commuting rate over the past   decade has taken a wild ride compared to the national and 70-city-average rates-evidence of a wide margin of error.

“It sucks,” said one city official who, for reasons of decorum, shall remain anonymous.

How to explain the change? Union member Daniel Kamalic volunteered to get to the bottom of it last week and contacted a policy analyst at the League of American Bicyclists, who then contacted friend Brian MacKenzie, Journey to Work Analyst for the U.S. Census. 

Kamalic’s first discovery was the fact that different base population numbers were used between 2009 and 2010, but MacKenzie said this would only account for a “slight” impact on commuting numbers. At first glance this is bad news for cyclists in the city, and the city itself, who have been working hard to make Boston a friendlier place to ride and get more cyclists on the road. The city has taught nearly 6,000 Boston Public Schools students how to ride and given away close to 1,000 bikes to low-income residents, and also helped fund the Boston Cyclists Union’s Bike to Market program, which fixed over 1,600 bikes in the last two years for free. With all that work going on, and more, the best answer to hear would be that it’s all a big mistake. And actually MacKenzie said that was a possibility, given the small sample size of the yearly American Community Survey (ACS).

“The number of bike commuters is still quite small for most places,” he said, “and will tend to result in large MOEs [Margins of Error], even in large cities, so dramatic swings across years are inevitable.”

This would also explain Boston’s erratic bike commuting levels over the past decade, but looking across the country, other cities are also reeling from the latest figures. Oakland, New Orleans, and St. Paul Minnesota all saw similar drops in bike commuting. And the national figure is down by 4%. And according to the ACS, Boston’s margin of error for the 2010 data is only 0.4 percent, so it likely does not explain all of the shift. MacKenzie said there could be other factors at play.  

“Even for large geographies–states, the nation–there is some evidence of real declines in bike commuting,” he said. “This may not be an accurate representation of workers’ willingness to bike to work, or may not reflect infrastructure modifications made to accommodate cyclists, but may be more a reflection of changes in travel behavior due to labor market shifts. That is, people calibrate where they live to where they work, and choose their transportation mode based on the relationship between home and work, so when workers lose their jobs or lose their homes, well-calibrated commuting patterns may be disrupted.”

But the good news is that over the last ten years Boston’s bike commuting numbers are still outpacing the nation, and an average of the top 70 cities, as the chart here shows. The trend for Boston is ever upward. With this kind of momentum, it’s likely this year’s 33 percent drop is merely a Boston-style pothole on the road to the world-class bike city we envision for the future.