We do not fully understand bicycling behavior and the influence of
infrastructure because our current data sources are limited. The
revealed preference studies cited above provide route information
based upon the respondent’s recall, but can be limited in sample size.
Most large sample surveys do not include questions about routes or
facility preferences. And, because bicycling is a rare activity, the
surveys still may not capture much bicycling activity. Health-related
surveys, such as the Behavioral Risk Factor Surveillance System,
typically have very large samples. However, until 2001 the questions
on physical activity focused on leisure-time activity, thus missing
bicycling for transportation . Another limitation of self-reported
travel data is that people often round-off their travel times to the
nearest 5-minute increment and overestimate travel times . These
surveys rarely assess total amounts of bicycling over more than one
day, making it difficult to estimate whether people achieve weekly
physical activity objectives.