1. II Institute of Theoretical Physics, University of Stuttgart, Pfaffenwaldring 57/III, 70550 Stuttgart, Germany
2. Xerox PARC, 3333 Coyote Hill Road, Palo Alto, California 94304, USA

Correspondence to: Dirk Helbing¹ Correspondence and requests for materials should be addressed to D.H. (e-mail: Email: helbing@theo2.physik.uni-stuttgart.de).

Advances in multiagent simulation techniques^{1, 2, 3} have made possible the study of realistic highway traffic patterns and have allowed theories^{3, 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.