Coherent moving states in highway traffic

Advances in multiagent simulation techniques1,2,3 have made possible the study of realistic highway traffic patterns and have allowed theories3,4,5,6 based on driver behaviour to be tested. Such simulations display various empirical features of traffic flows7, and are used to design traffic controls that maximize the throughput of vehicles on busy highways. In addition to its intrinsic economic value8, vehicular traffic is of interest because it may be relevant to social phenomena in which diverse individuals compete with each other under certain constraints9,10. Here we report simulations of heterogeneous traffic which demonstrate that cooperative, coherent states can arise from competitive interactions between vehicles. As the density of vehicles increases, their interactions cause a transition into a highly correlated state in which all vehicles move with approximately the same speed, analogous to the motion of a solid block. This state is safer because it has a reduced lane-changing rate, and the traffic flow is high and stable. The coherent state disappears when the vehicle density exceeds a critical value. We observe the effect also in real Dutch traffic data.