Numerical simulations for traffic-flow models on a decorated square lattice

We investigate a traffic-flow problem in a network of city roads. The network of city roads is assumed to be a square lattice with a decorated site on each bond; a car may locate at a usual lattice site or at a decorated site. We extend a traffic-flow model proposed by Cuesta et al. (Phys. Rev. E 51 (1995) 175) to models on the network of city roads and then study the models by using numerical simulations. We find that there is a phase transition of the first-order type from the free-moving phase to a traffic jammed phase, in general, in our models. In the traffic jammed phase, the average velocity of cars is larger for a model in which a traffic signal changes randomly, than for a model in which the traffic signal changes regularly.