Temporal transferability: trade-off between data newness and the number of observations for forecasting travel demand

Recent and large amounts of data are crucial for forecasting travel demand. However, in some cases, an older time point may have more data than a more recent time point. A trade-off between older data with a large number of observations and recent data with a smaller number of observations has not been investigated in the context of temporal transferability. In this paper, this trade-off is examined in the context of journey-to-work mode choice behaviours by utilising repeated cross-sectional data collected in Nagoya, Japan. Models estimated utilising different numbers of observations (ranging from 50 to 10,000) obtained at different time points (1971, 1981, and 1991) are applied to the forecasting of behaviours for 2001. Bootstrapping provides insights with statistical meaning. One finding is that the minimum number of observations from a recent time point that is required to produce a forecast statistically significantly better than that produced by older data with a larger number of observations is surprisingly stable, even when the number of observations from the older time point varies considerably. For example, 300–500 stable observations from 1981 produced forecasts that were statistically significantly better than that produced by 500–10,000 wide-ranging observations from 1971. Analysing the trade-off can help determine an efficient survey interval and sample size in an era of declining budgets for travel surveys.