  In this paper, two important factors which affect the pedestrian outflow at a
bottleneck significantly are studied in detail to analyze the effect of an
obstacle set up in front of an exit. One is a conflict at an exit when
pedestrians evacuate from a room. We use floor field model for simulating such
behavior, which is a well-studied pedestrian model using cellular automata. The
conflicts have been taken into account by the friction parameter. However, the
friction parameter so far is a constant and does not depend on the number of
the pedestrians conflicting at the same time. Thus, we have improved the
friction parameter by the frictional function, which is a function of the
number of the pedestrians involved in the conflict. Second, we have newly
introduced the cost of turning of pedestrians at the exit. Since pedestrians
have inertia, their walking speeds decrease when they turn, and the pedestrian
outflow decreases.
  The validity of the extended model, which includes the frictional function
and the turning function, is verified by both a mean field theory and
experiments. In our experiments, the pedestrian flow increases when we put an
obstacle in front of an exit. The analytical results clearly explains the
mechanism of the effect of the obstacle, i.e., the obstacle blocks pedestrians
moving to the exit and decreases the average number of pedestrians involved in
the conflict. We have also found that an obstacle works more effectively when
we shift it from the center since pedestrians go through the exit with less
turning.
