  In this paper, the impact of escaping in couples on the evacuation dynamics
has been investigated via experiments and modeling. Two sets of experiments
have been implemented, in which pedestrians are asked to escape either in
individual or in couples. The experiments show that escaping in couples can
decrease the average evacuation time. Moreover, it is found that the average
evacuation time gap is essentially constant, which means that the evacuation
speed essentially does not depend on the number of pedestrians that have not
yet escaped. To model the evacuation dynamics, an improved social force model
has been proposed, in which it is assumed that the driving force of a
pedestrian cannot be fulfilled when the composition of physical forces exceeds
a threshold because the pedestrian cannot keep his/her body balance under this
circumstance. To model the effect of escaping in couples, attraction force has
been introduced between the partners. Simulation results are in good agreement
with the experimental ones.
