The object of this paper is to make an exploratory investigation of the choice of different modes of transport when considering the total amount of travel, for all purposes, by an individual or group of the population. A new approach, called a model of 'modal mix', is outlined; this treats the cost and time characteristics of a mode not as constants but as variables related to the distance travelled by the mode as a proportion of the total distance travelled. If travellers attempt to minimise the generalised cost of travelling a given distance, the model predicts that in some circumstances division of the total distance between two modes will be preferred to the use of one mode only. In this it differs from the more common 'modal split' models, which typically assign a probability of travelling by one mode only for a particular category of journey. An empirical investigation is made to see whether the conditions necessary for the modal mix model to work in fact apply. It is found that there are indeed some features of the variations in bus costs and times, and car times, that support the theoretical approach. (a). For the covering abstract of the symposium please see irrd abstract no. 224453.
Samenvatting