Synchronized flow and phase separation in a two-lane cellular automaton model

This paper extends a cellular automaton model, named modified comfortable driving (MCD) model, to a two-lane roadway. A symmetric lane-changing rule set has been proposed (Set I). The fundamental diagram, the lane-changing frequency and spacetime plots are presented. It is found that for the two-lane model, there exists a density range in which phase separation between synchronized flow and wide-moving jams on one lane, and between light synchronized flow and heavy synchronized flow on the other lane, can be maintained for quite long periods of time. In this density range, (i) the outflow from jams is synchronized flow; (ii) wide moving jams are sparse. These are consistent with the empirical observation. We also investigate a slightly different lanechanging rule Set II in which stopped vehicles are not allowed to change lane. It is shown that in this case, the phase separation, between free flow and wide moving jams on one lane and between free flow and heavy synchronized flow on the other lane, can be maintained for sufficiently long periods of time. Consequently, the flux is enhanced comparing to that of rule Set 1.