  Dense granular flows through constrictions, as well as competitive pedestrian
evacuations, are hindered by a propensity to form clogs. We usesimulations of
model pedestrians and experiments with granular disks to explore an original
strategy to speed up these flows, which consists in including contact-averse
entities in the assembly. On the basis of a minimal cellular automaton and a
continuous agent-based model for pedestrian evacuation dynamics, we find that
the inclusion of polite pedestrians amid a given competitive crowd fails to
reduce the evacuation time when the constriction (the doorway) is acceptably
large. This is not surprising, because adding agents makes the crowd larger. In
contrast, when the door is so narrow that it can accommodate at most one or two
agents at a time, our strategy succeeds in substantially curbing long-lived
clogs and speeding up the evacuation. A similar effect is seen experimentally
in a vibrated two-dimensional hopper flow with an opening narrower than 3 disk
diameters. Indeed, by adding to the initial collection of neutral disks a large
fraction of magnetic ones, interacting repulsively, we observe a shortening of
the time intervals between successive egresses of neutral disks, as reflected
by the study of their probability distribution. On a more qualitative note, our
study suggests that the much discussed analogy between pedestrian flows and
granular flows could be extended to some behavioural traits of individual
pedestrians.
