Dissecting #BikeData

When the League first started analyzing the U.S. Census Bureau’s American Community Survey (ACS) journey to work data to publicize bike commuting rates across American cities, we included a 350-word disclaimer cautioning readers to take the data with a grain of salt. This year, we took to Twitter to parse out the good, bad, and surprising aspects of this year’s ACS bike commuter data. It was a lot more fun.

The major strengths of the ACS as an estimate of bicycling are that, 1. It comes out every year, and 2) It allows you to look city-level data. (If you are willing to wait for 5-year’s worth of surveys you can look at even small geographic areas, like Census block.) This allows us to look at change year over year in a particular city or region. Here’s Washington, D.C.’s impressive growth.

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That said, given that the ACS is sometimes under political attack, it’s worth giving it some love. Besides, how many other government agencies release reports like this? On the other hand, there are drawbacks. The ACS only counts commuters (journey to work); not every other type of trip. It only counts people; not the number of trips. It only counts people who chose the bike as their primary mode (what mode did you “usually” use?); not sometimes bicyclists, and not people who use transit, for example, for a larger part of their trip. It is only an estimate; one with sometimes very large margins of error. Because of that small sample size, it doesn’t do a good job of telling us who, demographically speaking, is biking.

The big take-way for me from the Twitter chat, was the need for communities to supplement the ACS with local bicycle counts. That will help will specific planning decisions. The ACS will give you an overall trendline and it’ll always be fun to look at and debate, but it’s not nearly enough.

In the meantime, we can all look forward to the planned 2015 National Household Travel Survey, which counts all trips, but isn’t as reliable at smaller geographies.

Here’s a recap of our chat last week: