Tuesday, September 23, 2014

Have we reached a plateau? Latest figures on bike commuting in Madison, Dane County, and Wisconsin

There is much anticipation in the bike advocacy world around the annual release of the American Community Survey (ACS) by the US Census Bureau. Among a wealth of other data on the US and its population, the ACS also asks by which means of transportation people get to work. I decided to look at the data for my home town, county, and state—Madison, Dane County, Wisconsin.

There are a multiple caveats on the data quality, but since there aren't many alternatives available, the ACS is still a valuable source of information of bicycle use and transportation trends. Some of the limitations become clear when we look at the actual question asked:
How did this person usually get to work LAST WEEK? If this person usually used more than one method of of transportation during the trip, mark (X) the box of the one used for most of the distance.
So someone who bikes to work on two days and takes her car on three would count as a car commuter. Similarly, a person who rides 5 miles to the commuter rail station, takes the train downtown, and then walks to their office, would count as a train commuter. The other, less obvious limitation, which is especially relevant for Madison, is that students' trip to their university are not considered commutes and therefore not counted. And of course, trips to work constitute only part of all trips made.

That said, let's look at the data, beginning at the state level.
Maybe unsurprisingly, at the state level the picture for bike commuting appears rather bleak. Between 2006 and 2013 the rate of bike commuters has been basically flat and far below one percent. However, one must keep in mind that there are only six states in the whole of the United States that have a mode share of one percent or more, and the national average is 0.62%. Nonetheless, the flat trend raises some uncomfortable questions for bike advocates.

 How do things look in Dane County? The proportion of people riding their bike to work is significantly higher than at the state level, and over the seven-year period there also is a small but noticeable increase in bike commuting.
This pattern repeats itself at a higher level in Madison. Given that Madison respondents make up roughly half of those of Dane County, this comes as no surprise. As you can see with the dotted lines in the charts, at the county and city level the margins of error are quite sizable, and conclusions about trends should be taken with a grain of salt. But when we compare the Dane and Madison data with cities with a similarly high rate of bike commuting, it appears that the growth in bike commuting may have plateaued over the past couple of years. Cities with a initially low bike commute share, such as New York City or Washington DC, continue their growth, but once the rate reaches around five percent, growth appears harder to attain.

I am not going to address the potential explanations for this plateau effect, but feel free to put forward your theories in the comments, especially as they pertain to the specific situation in Wisconsin and Madison. In the meantime I will try to get access to the Madison bike counter data, which would allow some cross-validation of the ACS data.


  1. A further complication of this data is adjusting for seasonality. I suspect that I'm not alone in looking at my bike as a primary mode of commuting during late spring, summer and fall; but mostly use my car in the winter. A lot would depend on when the survey was taken. Thoughts?

    1. The ACS states that the data is taken "monthly," which I assume means that the surveys are sent out at random over the course of the year and therefore seasonality should be averaged out. It could be, however, that this source of error is not factored into the larger margin of error that I have used in the charts.

  2. Reasons for the plateau? The first thing that comes to mind is that we may have reached the point where the easy and most productive changes have been made - striping lanes and designating streets as bicycle boulevards that were already de facto bicycle facilities, where a little official recognition helps new riders feel comfortable.

    I have observed that most new riders are people who happen to have moved somewhere where they can bicycle more, and one day realize that fact. That suggests that one way to break through the current plateau is to make sure the city/county/state are building more places where people can make the connection to bicycling. Unfortunately, the Bike Fed backed out of supporting smart growth back in 2008, and that may have reduced the growth potential in future years.

    1. I agree -- it's much easier to jump from 0.5% to 1% than it is from 5% to 10%. The typology introduced by Roger Geller makes a useful point: You have a very small proportion of people who will ride their bikes no matter what. Then there is a larger but still small group of people that can be enticed to ride by things like on-street bike lanes and an incomplete network of bike paths. But once you have these two groups riding, something different is required to get a mode share of more than 10%.

      Thanks for making the point about density and smart growth; can you say more about the Bike Fed's role there?