The fact that the process of evaluating travel alternatives is at once both rational and irrational may lead to the impression that it involves only a personal decision. Studies in this area have shown that a consideration of alternative courses of action is never undertaken in an “environmental vacuum” (Burkart and Medlik 1981; Chapin 1968, 1974; Cheek and Burch 1976; Cohen and Taylor 1976; Etzel and Wahlers 1984; Gold 1980; Hechet 1974; Heywood 1988; Kipnis and Mansfeld 1986; Longley 1984; Matley 1976; Robinson 1979; Nichols and Snepenger 1988; Pearce 1982; Timmermans 1984a). It is the social environment that is most often taken into account by the individual decision maker (Cheek and Burch 1976:189).