  A two--dimensional cellular automaton is introduced to model the flow and
jamming of vehicular traffic in cities. Each site of the automaton represents a
crossing where a finite number of cars can wait approaching the crossing from
each of the four directions. The flow of cars obeys realistic traffic rules. We
investigate the dependence of the average velocity of cars on the global
traffic density. At a critical threshold for the density the average velocity
reduces drastically caused by jamming. For the low density regime we provide
analytical results which agree with the numerical results.
