Long-term and short-term aspects of car allocation within the household context

Kurzfassung

Decisions concerning household car ownership and the corresponding usage by the household members have significant implications on fuel consumption and vehicle emissions. In this context, long-term and short-term choices which are strongly interrelated with one another play an important role. The long-term aspects involve the number of vehicles and different types owned by a household as well as the assignment of a main driver for each vehicle. The short-term dimension is represented by the vehicle allocation within a household at a daily level. In order to better understand the vehicle allocation process in the household context, the paper at hand investigates the importance of the longer-term and shorter-term components in this process and explores which one prevails. The study is based on data of the national household travel survey “Mobility in Germany” (MiD) of the year 2008, which collects behavioural travel data of entire households for all weekdays using a diary day concept. Initial analyses focus primarily on the long-term perspective. In this context, different discrete choice models which assign a principal driver to the available household cars are estimated. In order to study the interrelationship between the long-term and short-term aspects of the vehicle allocation process within a household, it is examined, whether the main driver of a car is, at the same time, the actual user on a trip. Attention is directed towards the trips where this is not the case, in order to understand what kind of trips (purpose, individual or joint travel, distance and duration, etc.) exhibit greater variability and in which cases households behave more flexible with respect to the allocation of vehicles. The paper provides a brief introduction about the background of the vehicle allocation process within the household context, taking into account its long-term and short-term aspects. The main part then concentrates on the corresponding empirical analyses, showing insights of ongoing work. The data used is described, followed by statistical explorations and the results of various estimated discrete choice models for the identification of a main driver and the allocation of a car, and accompanied by examinations concerning the actual usage of the assigned car by the principal driver. In particular, attention focuses on the discrepancy between long-term and short-term decisions concerning the allocation of cars within a household. Finally, conclusions are presented.