| Modeling dynamic activity generation is high on the research agenda in activity-based transport demand modeling. The concept of dynamic needs has been put forward as such a mechanism. The aim of this paper is to investigate which needs underlie the generation of discretionary activities such as social, recreational and sports activities. Three surveys were conducted to elicit, establish and analyze the needs. We carried out qualitative face-to-face interviews based on a laddering technique to reveal need dimensions using an exhaustive classification of discretionary activities. Quantitative approaches were then used to determine which needs are equivalent in terms of their effects on activities and, hence, can be merged. Finally, a questionnaire-based survey involving a large sample of individuals is used to measure personal levels of the needs identified and to correlate these measures with socio-economic and behavioral characteristics. In total, six independent needs emerged from this research, namely Physical exercise, Social contact, Relaxation, Fresh air / being outdoors, New experiences, and Entertainment. Many-to-many relationships between activities and needs support the hypothesis that substitution relationships may play a significant role in activity generation. This implies that current practice in activity-based modeling of focusing on activities may produce biased results when developing dynamic models of transport demand. Furthermore, the results show that personal levels on these needs correlate with various socio-economic as well as behavioral variables. |
