  The Nagel-Schreckenberg traffic flow model shows a transition from a free
flow regime to a jammed regime for increasing car density. The measurement of
the dynamical structure factor offers the chance to observe the evolution of
jams without the necessity to define a car to be jammed or not. Above the
jamming transition the dynamical structure factor $S(k,\omega)$ exhibits for a
given $k$-value two maxima corresponding to the separation of the system into
the free flow phase and jammed phase. Analyzing the $k$-dependence of these
maxima the backward velocity of the jams is measured. We find that the jam
velocity neither depends on the global density of the cars nor the maximal
velocity of the model.
