  Pedestrian groups are commonly found in crowds but research on their social
aspects is comparatively lacking. To fill that void in literature, we study the
dynamics of collision avoidance between pedestrian groups (in particular dyads)
and individual pedestrians in an ecological environment, focusing in particular
on (i) how such avoidance depends on the group's social relation (e.g.
colleagues, couples, friends or families) and (ii) its intensity of social
interaction (indicated by conversation, gaze exchange, gestures etc). By
analyzing relative collision avoidance in the ``center of mass'' frame, we were
able to quantify how much groups and individuals avoid each other with respect
to the aforementioned properties of the group. A mathematical representation
using a potential energy function is proposed to model avoidance and it is
shown to provide a fair approximation to the empirical observations. We also
studied the probability that the individuals disrupt the group by ``passing
through it'' (termed as intrusion). We analyzed the dependence of the
parameters of the avoidance model and of the probability of intrusion on
groups' social relation and intensity of interaction. We confirmed that the
stronger social bonding or interaction intensity is, the more prominent
collision avoidance turns out. We also confirmed that the probability of
intrusion is a decreasing function of interaction intensity and strength of
social bonding. Our results suggest that such variability should be accounted
for in models and crowd management in general. Namely, public spaces with
strongly bonded groups (e.g. a family-oriented amusement park) may require a
different approach compared to public spaces with loosely bonded groups (e.g. a
business-oriented trade fair).
