16: Possible Explanations for an Increasing Share of No-Trip Respondents

This chapter reports on some puzzling findings from the Danish National Travel Survey (DNTS). The DNTS was a continuous CATI survey conducted in the period 1992-2003 with 14-16,000 computer-assisted telephone interviews annually.

A continuous travel survey provides important information about changes in travel behaviour. Surprisingly, a decline in transport kilometres was observed in the DNTS in 1998 and an even sharper drop in 2001. The decline was registered for all transport means. Furthermore, the trip rate declined by twelve percent from 1995 to 2001. This trend in overall transport kilometres and trip rates is not found in other traffic observations. For instance, according to traffic counts collected by the Road Directorate, transport kilometres had in fact increased for many years until 2000 when they stabilised for a couple of years (Road Directorate, 2003). The DNTS changes are unlikely to derive from actual behavioural changes and are most probably explained by changes in the data collection methodology.