  We investigate the dynamics of the evacuation process with multiple
bottlenecks using the floor field model. To deal with this problem, we first
focus on a part of the system and report its microscopic behavior. The system
is controlled by parameters of inflow and the competitiveness of the
pedestrians, and large inflow leads to a congested situation. Through
simulations, the metastable state induced by conflicts of pedestrians is
observed. The metastability is related to the phase transition from free flow
to congestion. The critical condition of the transition is theoretically
derived. In addition, we give simulation results of situations with multiple
bottlenecks. They imply that local improvement of pedestrian flow sometimes
adversely affects the total evacuation time, and that the total optimization of
the system is not straightforward.
