Review of evidence for temporal transferability of mode-destination models

One main motivation for developing travel behavior models is to use them to forecast future levels of transport demand. Given that the interest in transport planning is often in long-term forecasts, with forecast horizons of up to 30 years, it is important to consider the transferability of travel behavior models over time. The importance of model transferability has been recognized since disaggregate models were first applied in the late 1970s and early 1980s, but seems to have been largely forgotten recently, because the focus has been on the development of ever more advanced models that better explain current behavior, with a particular focus on the representation of taste heterogeneity. However, there are sufficient grounds to suspect that the model that best explains current behavior may not necessarily be the best tool for forecasting, not least because of the risk of overfitting to the base data. This paper aims to return the crucial issue of temporal transferability of travel demand models to the research agenda. First, the notion of transferability is discussed, highlighting the potential impacts of violations of the assumption of transferability, and the way transferability can be assessed is also described. Next, the most complete review of existing work investigating the temporal transferability of mode and mode-destination models to date is presented. Finally, a number of areas in which future research should be directed are identified.