Grease in the numbers
To be clear, I wish it were true that bicycle commuting was up that much. I think Pittsburgh has a great bike history, a lot of great bike amenities, has had some great bike leadership, and I have no doubt a great bike future. But +269%? Maybe.. but also possibly maybe not.
The literal number of bicycle commuters for the City of Pittsburgh reported in the 2010 American Commutny Survey (ACS) was 2,267. The margin of error reported with the ACS on that specific number was +/- 824. Big range there. Again, the large relative error is due to the small size of the city and the really small size of bicycle commuters. The ACS is a sample frame of roughly one in 100 households in the general population annually.. higher oversampling happens for smaller groups or smaller geographic areas. So the 2010 data the reported 2,267 bicycle commuters living in the City of Pittsburgh likely comes from the survey capturing just a couple dozen bicycle commuters. Not a lot to work with.
So what has the ACS been telling us year in and year out? Here are all of the comparable ACS results on bicycle commuting of City of Pittsburgh residents. ACS results before 2006 did not include Group Quarters population and so I would not consider them comparable to the others. Shown are just the ranges made up of the estimates plus or minus the reported standard errors. The ACS reports different data based on compilations of data over 1, 3 or 5 years. The 3 and 5 year compilations have more data and thus smaller proportional sample errors than the 1 year estimates.
So a lot of confusion over any one point estimate is the fault of the Census Bureau resulting from the elimination of the long form of the Decennial Census. The result is that we are all going to be forced to rely on data from the American Community Survey(ACS) for most all data like this. The problem is that as a survey, there are limitations that are not always appreciated. The message the Census Bureau tells a lot of folks like me to spread is that you have to take into account that smaller areas and in particular smaller populations can have results significantly impacted by sample error and other issues. Bicycle riders are a small population for sure.
Clearly there was a big jump for sure from 2000 when the reported number of bicycle commuters was 627. In absolute numbers that works out to a percentage increase far larger than +269%. Not clear to me from what I have read on what the 269% refers to specifically actually. The actual increase could actually be higher depending on what is being measured.
This is all a good learning exercise on how to use ACS data which will be coming out nearly continuously from now on. If you think that the number of bike riders is relatively stable, or at least changing in a consistent way then reconsider the graph above. Reality probably does not jump around all that much. So yes, all of those ranges show an increase over 2000. When that growth happened is another question altogether. If you look at the high end of the range in 2007 and the low end in 2010, it is at least conceivable that the number of bicycle commuters has gone down over that time.
Over the decade though, the number of post-secondary students in the city proper has gone up a lot. Those folks are disproportionately non-auto drivers. If students report that they are working as many are even if part time, they will be asked their mode of commuting and in most cases their response will be included in the results for commuting data. With something on the order of 10K more undergraduate or graduate students living in the city since 2000, I have to believe they are a big chunk of the increase in bicycle commuters showing up in the data.