@granul3].

Depending on the choice of parameters, the cellular automaton (CA) model introduced in [@ourpaper; @PED01a; @PED01b] is able to reproduce many of the observed collective effects of pedestrian dynamics, i.e. panicing and herding behaviour [@aki0]. In this paper the model is extended by a friction parameter $\mu$, which allows an improved description of clogging and stucking phenomena of pedestrians. It will be shown that conflicts and friction are responsible for several interesting effects which become especially relevant in high density situations, e.g. during evacuation processes, and that they are important for a correct reproduction of the dynamics. We start with a short summary of the model’s basic concepts and its update rules.

Basic principles of the model
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The model considered here is a CA where the space is discretized into small cells which can either be empty or occupied by exactly one pedestrian. Each of these pedestrians can move to one of its unoccupied neighbour cells (see fig. \[trans\]) at each discrete time step $t\to t+1$ according to certain transition probabilities.

![Definition of the transition probabilities $p_{ij}$.[]{data-label="trans"}](\DIR/fig1.eps){width="0.65\columnwidth"}

The probabilities are given by the interaction with two discrete [*floor fields*]{}, $D$ and $S$ [@ourpaper; @PED01a; @PED01b; @aki0]. The field 