  The relative dynamics in collision avoidance between individual pedestrians
and dyads has been recently studied, and it was shown that individuals may
intrude dyads that are not socially interacting. Building on this, our current
study examines how much each party contributes to collision avoidance by
measuring deviations from their intended paths. Our findings suggest that
individuals prioritise trajectory efficiency in undisturbed situations, but
prioritise safety when encountering dyads, deviating more from their intended
path. Non-interacting dyads present a similar behavior, although their
trajectories appear to be even more efficient than those of individuals in
undisturbed situations, and their deviations during encounters less pronounced.
On the other hand, socially interacting dyads are not very efficient in
undisturbed situations, and their behavior is mostly unaffected by encounters.
These results strongly suggest that group dynamics affects in two ways the
behavior of pedestrians, namely it has a dynamical and a social effect. The
dynamical effect stabilises their trajectory, while the social one decreases
the ability to focus on the external environment, leading to reduced efficiency
and safety. Another finding concerns the tendency of individuals to avoid in a
more prominent way the interacting dyads as compared to non-interacting ones.
This suggests that individuals may assess others' contribution to collision
avoidance. An impact parameter analysis reveals that collision risk influences
path deviations in pedestrian encounters. For individuals, larger behavioral
differences between low and high interaction levels of the dyad occur both when
the collision risk is high and during less critical encounters. For dyads, the
deviation differences between low and high interaction levels are most
pronounced when the individual is on course to pass close to the dyad.
