  We investigate the role of conflicts in pedestrian traffic, i.e. situations
where two or more people try to enter the same space. Therefore a recently
introduced cellular automaton model for pedestrian dynamics is extended by a
friction parameter $\mu$. This parameter controls the probability that the
movement of all particles involved in a conflict is denied at one time step. It
is shown that these conflicts are not an undesirable artefact of the parallel
update scheme, but are important for a correct description of the dynamics. The
friction parameter $\mu$ can be interpreted as a kind of internal local
pressure between the pedestrians which becomes important in regions of high
density, ocurring e.g. in panic situations. We present simulations of the
evacuation of a large room with one door. It is found that friction has not
only quantitative effects, but can also lead to qualitative changes, e.g. of
the dependence of the evacuation time on the system parameters. We also observe
similarities to the flow of granular materials, e.g. arching effects.
