Highway
Car Traffic as a Complex System:
The
Physicist’s Point of View
A
simple cellular automaton model of highway car traffic flow will be presented.
This system exhibits a second-order phase transition between the free-moving
phase and the jammed phase. Using concepts borrowed from the theory of phase
transitions in statistical physics, it can be shown that random braking is the
symmetry-breaking field conjugate to the order parameter. For a given value of
the speed limit, it is then possible to determine the values of the usual
critical exponents using computer simulations. These numerical results can also
be obtained within the framework of an approximate technique going beyond the
mean-field approximation. It can be shown that the critical exponents satisfy a
scaling relation, which can be derived assuming that the order parameter is a
generalized homogeneous function in the vicinity of the phase transition point.