Information about the variability of public transport usage over time is an important input to many studies and to the design of before and after surveys attempting to measure changes in public transport usage as a result of a policy change or project implementation. Unfortunately, most travel surveys collect only one day of travel data from each respondent, therefore providing no information on temporal variability. This paper examines this issue from two data perspectives. Firstly, a detailed analysis of data from the 42-day MobiDrive survey conducted in Germany in 1999 was used to measure variability in public transport usage at an individual and household level. Secondly, data was used from an origin-destination survey on 38 bus routes over a 52-day period in Melbourne in 1994 to estimate variability in public transport usage at a route level. Several findings from these analyses are considered of importance. Firstly, the variability in public transport usage over time is significant, and belies the notion that there are just two groups, "users" and "non-users". There is a significant third group, the "sometimes users". Secondly, the variability in usage (as measured by the Coefficient of Variation) is a function of the level of usage. Thirdly, the variability is a function of the level of aggregation of the data, with individuals having more variability than households or routes. While some of these findings are intuitively obvious, this paper serves the purpose of quantifying the magnitude of these effects. The paper concludes by examining the sample size implications of these findings for longitudinal surveys of public transport usage. For the covering abstract see ITRD E126595.
Samenvatting