Coherent moving states in highway traffic

Advances in multiagent simulation techniques(1-3) have made possible the st udy of realistic highway traffic patterns and have allowed theories(3-6) ba sed on driver behaviour to be tested. Such simulations display various empi rical features of traffic flows(7), and are used to design traffic controls that maximize the throughput of vehicles on busy highways. In addition to its intrinsic economic values, vehicular traffic is of interest because it may be relevant to social phenomena in which diverse individuals compete wi th each other under certain constraintsg(9,10). Here we report simulations of heterogeneous traffic which demonstrate that cooperative, coherent state s 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 spe ed, analogous to the motion of a solid block. This state is safer because i t 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.