F. Sharmeen et al.
of challenges remain on the future agenda. A first challenge is to negate the idea that personal social networks
are stagnant. So far, social networks in transportation research have been studied as if they were. On the contrary,
it is indeed very much dynamic. People’s social network size and composition change over time, sometimes
triggered by lifecycle events, such as changing household composition, job or home location. The contemporary
shift in travel behavior analysis towards dynamics necessitates the inclusion of social network dynamics. The
concept has been coined recently [5].
Regarding data collection on social networks and social activity-travel patterns still some challenges remain
as well. To get a good impression of the heterogeneity of leisure activities, it is desirable to collect longitudinal
diary data. Traditional travel diary surveys collect one or two days of travel data from participants. While cross-
sectional travel diary surveys are useful in determining the overall average travel behaviour of the regional pop-
ulation, they do not capture repetitive patterns in social activities, for instance weekly routines of people. New
GPS technologies provide a promising way of collecting longitudinal travel data without asking too much effort
from respondents.
In addition, the study of the effect of ICT’s on social activity-travel remains a topic for future research. Al-
though this topic has been studied recently [4] [9], the possibilities of ICT’s are increasing rapidly. These
changes will affect social travel, for instance in arranging a social trip (e.g. making reservations, buying tickets,
checking routes, weather and travel conditions), making additional research necessary.
A further challenge is to link the a-spatial aspect of social network to the spatial one. There is a spatial facet
attached to an individual’s social network as far as travel and transportation is concerned. The distance and ac-
cessibility of the peers should matter in planning and maintaining social networks [10]. This topic has been
largely overlooked by contemporary research. The social environment should not be studied in isolation from
the geographical environment.
Finally, the ageing of the population is a topic that deserves future research with regard to social networks and
travel behavior. On average, older people have more leisure time compared to younger (working) people. They
may therefore spend more time on social activities. On the other hand, the elderly on average have a smaller so-
cial network and may be less mobile. Social network analysis can give relevant insights in social activity-travel
behavior of senior citizens, as well as matters of accessibility, social capital and social equity.
The analysis of social networks has a far reaching potential in understanding almost all aspects of human be-
haviour. These potentials have been realized for long. A recent growing field of exploration is activity and travel
behaviour. The history of social networks and transportation literatures is nonetheless in an exploration stage.
There have been some commendable works already. Further comprehension and integration of the local social
context, social externalities and social dynamics to the travel behaviour models remain on the contemporary
agenda.
References
[1] Axhausen, K.W. (2005 ) Social Networks and Travel: Some Hypotheses. In: Donaghy, K.P., Poppelreuter, S. and Ru-
dinger, G., Eds., Social Aspects of Sustainable Transport: Transatlantic Perspectives, Ashgate, Aldershot, 90-108.
[2] Carras co, J. and Miller, E. (2006) Exploring the Propensity to Perform Social Activities: A Social Network Approach.
Tra ns por tat ion , 33, 463-480. http:/ /d x. doi .o rg/1 0. 10 07 /s11 1 16 -006-8074-z
[3] Dugundji, E. R . , Páez, A., Arentze, T.A., Walker, J.L. Carrasco , J. A. Marchal, F. and Nakanishi, H. (2011) Transporta-
tion and Social Interactions. Transportation Research Part A: Policy and Practice, 45, 239-247.
http://dx.doi.org/10.1016/j.tra.2011.01.001
[4] van den Berg, P., Arentze, T. and Timmermans, H. (2013) A Path Analysis of Social Networks, Telecommunication
and Social Activity-Travel Pat terns. Transportation Research Part C, 26, 256-268.
http://dx.doi.org/10.1016/j.trc.2012.10.002
[5] Sh armeen, F., Arentze, T. and Timmer mans, H. (2010) Modelling the Dynamics between Social Networks and Activi-
ty-Travel Behavior: Literature Review and Research Agenda. Proceedings 12th World Conference on Transport Re-
search, Lisbon, 11-15.
[6] Arentze, T. and Timmermans, H. (2008) Social Networks, Social Interactions, and Activity-Travel Behavior: A Frame-
work for Microsimulation. Environment and Planning B: Planning and Design, 35, 1012-1027.
http://dx.doi.org/10.1068/b3319t
[7] Ronald, N., Dignum, V., Jonker, C., Arentze, T. and Timmermans, H. (2012) On the Engineering of Agent-Based Si-
mulations of Social Activities with Social Networks. Information and Software Technology, 54, 625-638.