The demand models used in literature, in the field of a behavioural approach, generally simulate the user choices through a discrete choices model.The consolidated approach is not explicitly able to simulate the variation of choice probability, in consequence of the different events, which characterize the evolution of transportation system. So, in this note, two types of model are defined: static demand models the models that give the choice probability of the single alternative, independently of the actual choice of the decision-maker, relative to the actual system condition; and dynamic demand models the models that give the choice probability accordingto the actual and the previous system condition, considering change and earlier decisions. The need to introduce dynamic models regards different main decisions, among which it is possible to recall: the path choice, for a private transportation system user; the run choice, for a transit systemuser, considering the travel choices; and the ownership choice and particularly the ownership decision of vehicles, considering the mobility choices. Predominantly, the models used in this area of research are members of the family of discrete choice models, derived from the random utility theory. This theory is based on the hypothesis that every individual is a rational decision maker, maximizing utility relative to his own choices. Different discrete choice models are obtained from different specifications of the joint density of the random vector. The models used in literature are:the Generalized Extreme Value (GEV) model; the Probit model; the ordered GEV model and the Mixed Multinomial Logit model. The most used from researchers and practitioners is the Multinomial Logit model. These mathematicalmodels have been applied in a way that does not represent adequately the dynamic of the choice process, emphasizing the systematic and invariant aspects of choice behaviour, which are assumed to dominate the choice process. In particular, they do not represent explicitly the influences exercised by the previous decisions on the actual choice. In literature, the knownmodels that consider the effects of the previous choices are the car ownership models. Many of these studies simulate the car ownership choices using the Multinomial Logit model and introduce the parameter transaction search cost, in order to consider the influence exercised by the previous choices. A previously developed series of linked choice models to explain household vehicle ownership and adjustments in ownership over time is discussed. The effects of the experience are considered introducing the brand loyalty and the parameter experience index, which is a summary of retrospective utility. The vehicle type choice is simulated using a Mixed MultinomialLogit model. This represents the effects of the experience through the brand loyalty and the random components, and is able to consider their endogeneity. However, these models are based on static (or pseudo-dynamic) structures. The transition matrix, which represents the variation of user decisions over time, and the sequential model, which represent the time dependencies of path choice, has suggested the vehicle transition choice model. According to the sequential approach, the model simulates the permanence or the transition of the actual system state. It is different from the pseudo-dynamic models, because it simulates explicitly the choice of an alternative, in a given period of time, conserving or modifying the choice set relative to the previous period. The time-dependencies are considered introducing some attributes that are function of the past state. At first, the proposed model has been applied to the holding vehicle, in order to compare the results obtained with the experimentation of the pseudo-dynamic models, used in literature. The model has been specified, calibrated and validated using: a database relative to the socio-economic evolution of a sample family, which captures dynamic longitudinal effects; a database relativeto the technical classification of vehicles, defined by a company of car rent; a database relative to the technical-performances characteristics ofvehicles, obtained by a specialized car review published in Italy. The results obtained from the experimentation of the transition model are presented in the paper with the results obtained through the application of the models used in literature. The comparison gives a favourable result for the transition model in relation to the other experimented models. For the covering abstract see ITRD E137145.
Samenvatting