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The Model

In this section, we will give a short description of the main parts of the suggested model. However, it was considered important to include the main points in this chapter, in order to introduce the reader to the overall context of endogenous dynamics and the key role of emotional responses and memory-activation mechanisms. In this way, the simulation results that follow in the next section will become clearer.

Furthermore, at this point, it should also be stated that the structure of the described model is based to a great extent on the work of Han et al. on the modelling of dynamic choice sets of shopping locations (Han, Arentze, & Timmermans, 2007; Han, Arentze, Timmermans, Janssens, & Wets, 2009). The model extends this work, as it does not focus only on the shopping activity type; it models the choice set formation of activity profiles, which constitute combinations of several activity attributes, and models apart from the short-term dynamics, the point of time that a long-term adaptation is considered.

Activity Profiles and Universal Choice Set

In the context of this model, it is assumed that when an individual travels in order to reach an activity location, (s)he actually chooses from his/her choice set an activity profile and implements it. An activity profile consists of a combination of states of various activity attributes (Arentze, Ettema, & Timmermans, 2007). For instance, two examples of activity profiles that could be included in the choice set of an individual follow:

• Shopping, supermarket, going by car, starting-time of trip at 17:00, origin of the trip: office, via route A

• Shopping, grocery shop, going by bike, starting-time of trip at 18:00, origin of the trip: home, via route B

When an activity profile is habitually followed by an individual, it is considered to be a script that is repeatedly implemented when an activity needs to be conducted. A universal choice set includes all the feasible activity profiles that an individual can select. Therefore, for every activity type that is included in an individual's agenda and under every specific context-condition (e.g. weekday and rush-hour), there is a universal choice set of possible activity profiles. Undoubtedly, this universal choice set is directly influenced by the long-term decisions of that individual, such as the work and residential location, the number of available cars, etc.

However, when an individual is engaged in the decision-making process and needs to choose one specific activity-profile, usually (s)he does not consider all the activity profiles that are included in the universal choice set. Instead, (s)he considers a subset of it, which constitutes the choice set of that individual at this specific point of time, under the specific context-condition and for the specific activity type. In the following section the modelling of this dynamic process of choice set formation is explained.

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