  This study presents an experimental measurement of pedestrians' body rotation
in bidirectional streams. A mock-up corridor monitored using a camera placed on
azimuthal position is used to study pedestrians' behavior in unidirectional and
bidirectional flows. Additionally, a commercial tablet is fixed on the chest of
sample pedestrians to examine their body rotation (or yawing) which cannot be
obtained using position tracking alone. Angular velocity is recorded and
simultaneously stored in a central location using a wireless network, thus
allowing the analysis of body movements with a high sampling rate and a limited
delay. To investigate the influence of major/minor flow proportion (flow-ratio)
on bidirectional streams two different situations were tested: the balanced
configuration (with equal flows in both directions) and an unbalanced
configuration (with different major and minor flow). Results clearly show that
unidirectional flow is more stable compared to the bidirectional case,
requiring less time to cross the experimental section and showing a very small
amount of rotation during the whole experiment. Both bidirectional
configurations showed high values of body rotation, in particular during lane
formation and dissolution. Finally, rotation directly measured on pedestrians'
body was compared with the one obtained indirectly by analyzing pedestrians'
trajectories. The comparison shows that, at least from a qualitative point of
view, both methods are in agreement, thus suggesting that even properties which
can only be measured by motion sensing could be obtained indirectly through the
analysis of trajectories. Concluding, it has been suggested that while lanes
help smooth out bidirectional flows, larger instabilities are observed compared
to the unidirectional case. Lane separation and/or appropriate guidance are
therefore required.
