
Research interests
Pedestrian traffic

I have been part of the PEDIGREE project on pedestrian traffic.
We have realized several experiments in various settings,
including bidirectional traffic in ring corridor, onedimensional
motion on a circle, binary or multiple interactions of pedestrians,
oscillations at a bottleneck, etc.

Data analysis

With Asja Jelic, and in collaboration with the
other teams of the PEDIGREE project, we have
analysed the experimental data obtained for
the onedimensional flow of pedestrians.
Microscopic features as well as macroscopic ones
could be extracted.

The relation between velocity and headway
has been shown to exhibit two sharp unexpected
transitions in the following behavior:
while for large distances pedestrians move
at their preferred velocity, they need to
adapt to their predecessor when the distance
decreases below 3m.
This adaptation occurs on a time scale which
suddenly shrinks when the distance becomes
less than 1.1m.

The relation between step size and velocity
was shown to be very different from the one
found in locomotion studies. Indeed,
in the latter, only isolated pedestrians
are considered, while in our case the lowest
velocities result from steric constraints
due to the presence of other people.

Modeling

From experimental data obtained for a
onedimensional pedestrian flow, in a collaboration
between 3 teams of the PEDIGREE project, we found
that the best correlation between the acceleration
of a pedestrian on the one hand,
and a function of the velocity
difference / distance with its predecessor on the
other hand, was
obtained only if the following observation was taken into account:
while a pedestrian can determine almost instantaneously the distance to its predecessor, it needs
more time to evaluate the velocity difference.
Based on this observation, we have proposed a
pedfollowing model able to reproduce both the
heterogeneities and the wave propagation that
occurs in quasionedimensional pedestrian flows
(corridors).

In collaboration with IMT, we have also proposed
a macroscopic model for bidirectional flows in corridors.
This model reproduces several features of the
experiment realized in a ring corridor by the
PEDIGREE project, qualitatively and quantitatively.

In collaboration with IMT, we have more recently
proposed some 2D pedestrian models derived
from microscopic models.

Chevron effect

When two perpendicular pedestrian flows are crossing each
other, some diagonal patterns were known to occur.
In his PHd, J. Cividini (in collaboration with H. Hilhorst
and C. AppertRolland) has shown, in the frame
of a model based on exclusion processes, that this diagonal
pattern was produced by a linear instability.

Besides, J. Cividini has evidenced an unexpected
nonlinear effect,
namely that the diagonals are not completely straight lines,
but rather have the shape of chevrons.
He has shown that indeed, the dynamics of the system
could sustain a non linear mode with this chevron structure.

This chevron instability could also be understood
in terms of an effective interaction between pedestrians
of the same type, mediated by the perpendicular flow.
This result can also be seen as a contribution to the
large field of effective interactions in soft matter.
Here it is the first example of such an interaction
in out of equilibrium systems, that can be solved
exactly at the microsopic scale.
