Car Availability: Accounting for Temporal Variations
RICHARDSON T, Royal Melbourne Institute of Technology, Australia and AMPT E, Steer Davies Gleave, UK
Many models of travel demand, particularly models of mode choice, have assumed that the choice of mode is often highly constrained, with many users being captive to certain modes because of economic or social circumstances. In particular, many studies hav
Many models of travel demand, particularly models of mode choice, have assumed that the choice of mode is often highly constrained, with many users being captive to certain modes because of economic or social circumstances. In particular, many studies have noted that those people without access to a car are the most predominant users of public transport, particularly in off-peak times.
However, most of these studies have defined "car availability" in a rather simplified manner. Specifically, most studies have used 'household car ownership" as the major measure of "car availability", and have classified households as "non-car-owning", "single car households", and "multiple car households". Some more advanced studies have considered the number of people in the household to obtain a "cars per person" ratio, and have used this measure to explain variations in trip generation and mode use.
This paper takes the view that "car availability" should mean "was a car available to a particular person at the time when that person wanted to make a trip?" For example, if the family car is parked at a workplace during the day when someone at home wants to go shopping, then that person has no "car availability" at that time. This paper uses data from the 1994 Victorian Activity & Travel Survey (VATS) to calculate true measures of "car availability by tracing the location of household cars during the day and matching this with the travel demands expressed by members of the household. It is shown that, depending on the definition used, the level of "car availability" may be substantially overestimated or under-estimated by conventional measures, and that this over- estimation or under-estimation is not distributed uniformly across social and economic groups in the community.
The paper demonstrates that some commonly held beliefs about car availability and car ownership can be seriously questioned when viewed from the perspective of "car availability" for a particular trip.
Association for European Transport