social learning on individuals’ choice making and behaviour have not been investigated in the transport context. This paper introduces the use of a laboratory experiment for exploring the effects of social interaction on travellers’ choice making and behaviour. A hypothetical employer-based demand management initiative to reduce employees’ car use, which is framed as a social dilemma situation, is used in the experiment. One of the main features designed into the experiment is a social interaction feature for participants to communicate and exchange information in a repeated decision making environment. The paper is structured as follows. Section 2 briefly reviews relevant studies of social interaction and social learning in travel behaviour and explains the types of social interaction and social learning studied in this paper. Section 3 describes the detailed design of a laboratory experiment to explore the effects of social interaction on travellers’ behaviour, while Section 4 presents the results of a small-scale experiment run. Section 5 discusses the implications of the results and Section 6 highlights further useful studies that may follow from this study. SOCIAL INTERACTION AND SOCIAL LEARNING Jones and Sloman (2003) argued that the existence of the ‘snowball effect’, a phenomenon where long-term effects may be greater than short-term ones, increases the effectiveness of travel demand management measures over time. They stated that there is some evidence that changes may be slow at first, but then accelerate as people see their colleagues and neighbours changing their travel behaviour. Exploring the implementation of voluntary household travel behaviour change
(e.g. to give high level of contribution when others make low contribution). The numbers of ‘suspected’ free-riding occurrences are quite high: 28% (14 out of 50) in Treatment 2 and 34% (17 out of 50) in Treatment 3. The numbers of occurrences of pro-social behaviour are lower (16% of rounds (8 out of 50) in Treatment 2 and 24% of rounds (12 out of 50) in Treatment 3). However ‘partial’ consensus, where two of three group members make the same choice, occurs on many occasions (66% of rounds (33 out of 50) in Treatment 2 and 79% of rounds (35 out of 50). In summary, social learning through communication has been used by some participants to optimise collective outcomes (by contributing high) but it has also been used by some others to optimise their individual outcomes (by ‘free-riding’ on others’ contributions). This shows that both cooperators and ‘free-riders’ exist in the experiment. In line with this finding, a relevant study using a one-off experimentation by Fischbacher et al. (2001) showed that a fraction of people are conditional cooperators (50%), another fraction are ‘free-riders’ (30%) and the other fraction are either ‘hump-shaped’ contributors or display no patterns. 4.2 Analysis using learning models To study the existence of confirmation and conformity models of social learning, thus testing Hypothesis 3, the choices of individuals in Treatments 2 and 3 are analysed. We decide to use a simple method for modelling participants’ choice making, which is based on the probability of a choice being made by an individual. The higher the probability is, the more likely the choice will be selected. These probabilities are obtained using learning models, which include both individual learning and social learning models.