Analysis of phase transition of traffic flow in a two-layer network via cellular automaton model

We propose an idealized cellular automaton model of two-layer traffic system coupled with ramps. The motions of vehicles in the two layers are, respectively, described by the rules prescribed in the Biham-Middleton-Levine (BML) model. By simulation it is found that the density of ramps and the non-uniformity of initial vehicle density distribution between the two layers have remarkable influence on the phase transition from. the free-flow phase to the jamming phase. For suitable parameters, there might occur the phenomena of slowing down in the phase transition and the so-called local and global phase transitions.