By Robb Davis

Just after Davis was named, for a second time, a “Platinum Bicycling City” by the League of American Bicyclists, results of the 2010 American Community Survey showed that 22 percent of Davisites commute to work by bicycle.

The survey is conducted by the U.S. Census Bureau and is based on a relatively small sample, and thus the actual percentage is most likely between 15 and 29 percent. Despite these margins, no other city surveyed — including sister platinum cities Portland and Boulder, Colo. — come close to reaching this rate.

While statistics like this might merely tell us what we already know about our bicycling habits, what do they really tell us about how much we are cycling for all the trips we make?

After all, commuting is only one type of transportation. And while many adults engage in it most weekdays, it excludes trips made for other reasons and those made by the large numbers of community members not covered in the survey — notably children, seniors and students.

Just pause for a moment and think about all the trips taken by members of your household in the past week. There are trips taken by children going to school or to after-school activities; trips taken for shopping, entertainment or to attend religious services; and trips taken merely for exercise. By some estimates, fewer than 20 percent of all trips are taken to get to work.

We know that 22 percent of us commute by bike but what do we know about our “bicycle mode share” for all the trips we make? You might be wondering why this matters.

Our city’s Bicycle Plan, adopted in 2009, set a goal that we will use bicycles for 25 percent of all trips taken in Davis by 2012. Further, we know transportation accounts for about 50 percent of our carbon emissions and that our Climate Action Plan has a vision that by mid-century, 50 percent of all trips taken in Davis will be by a means other than automobile.

Despite having some information from various studies, we lack a clear estimate of how much we are riding our bikes for all trips. Thanks to UC Davis’ annual campus travel survey, we know that, on an average weekday, 41 percent of those arriving on campus arrive by bicycle.

We also know that in recent years, 18 to 25 percent of elementary students travel to school by bike and that a third of students surveyed recently at Davis High School said they typically come to school on two wheels. These numbers indicate we may be approaching our targets but none of them enables us to accurately assess mode share for all trips.

To assess our bicycle mode share — as well the share of all other modes — we need to conduct a full mode share study. One approach, used by Boulder every two to three years since 1990, selects a random sample of residents who fill out a full “travel diary” for a single, randomly selected day. Because this method requires respondents to track every trip (long and short) for a day, it provides a detailed picture of the travel modes they use for all activities.

Randall Rutsch, a senior transportation planner in Boulder, reports that these studies have been instrumental in enabling the city of Boulder to set and evaluate transportation goals. The longitudinal nature of the surveys has enabled Boulder to examine whether transportation policies are moving the city toward its goal of reducing single-occupancy vehicle mode share.

The travel diary method is one way to assess mode share and may be cost-prohibitive. However, it is time for Davis to implement a mode share survey to guide our transportation policy decisions in the years ahead.

To that end, the City Council should develop a partnership with the Institute for Transportation Studies and the Sustainable Transportation Center at UC Davis, Unitrans and community groups such as Davis Bicycles! to conduct its first full mode share study in 2012.

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