A comparative study of contact frequencies and modes among social network members in four countries.

Social activities are responsible for a substantial portion of trips (Axhausen, 2005). Related trips, intending to allow social activities, are influenced by new ways of social interaction, oc-curring since the rise of new information and communication technologies. Urban and transport planners need to take these changing communication patterns into account as they impose new demands on urban environments and transportation services. Therefore, it is im-portant to study face-to-face interactions, implying physical movements, as well as ICT-mediated communication patterns for social purposes, that do not rely on travel. From a social network perspective, a certain amount of contact between two persons is nec-essary to maintain their social tie. This contact can include face-to-face meetings as well as contacts mediated by different ICT tools. In recent years the possibilities for ICT-mediated contacts have increased tremendously. This will have an effect on face-to-face interactions and therefore also on travel. Regarding the effects of ICT on activity travel patterns generally four options are possible: substitution, complementarity, neutrality and modification (Salo-mon, 1986; Mokhtarian, 1990; Graham and Marvin, 1996). Previous studies have shown that, for leisure or social activities, the effect of ICT is generally complementary (e.g. Mokhtarian and Meenakshisundaram, 1999; Senbil and Kitamura, 2003; Mokhtarian et al., 2006; Wang and Law, 2007; Frei and Axhausen, 2008; Mosa et al., 2010; van den Berg et al., 2012; Car-rasco, 2011). Lately, the relationship between ICT and travel patterns has received a substantial amount of attention in the literature on travel behaviour. However, still little is known regarding the effect of ICT on travel for social activities. Thus far, the relationships between communication patterns by different ICT-mediated modes, face-to-face interactions for leisure purpose and travel have been largely neglected in the travel behaviour literature. Recently, data collection efforts have been developed that can bridge this gap, namely in Toronto, Canada by Hogan et al. (2007), in Zurich, Switzerland by Frei and Axhausen (2007), in Eindhoven, the Netherlands by Van den Berg et al. (2009), in Switzerland by Kowald and Axhausen (2012), in Concepción by Carrasco and Cid-Aguayo (2012) and again in Zurich, Switzerland, by Guidon and Axhausen (2017).