Moving Like a Solid Block

Highway traffic is both a social phenomenon and a source of data for understanding the dynamics of systems made up of many individuals following their own behavioral rules. We present computer simulation results that point to the existence of a new and general phenomenon in mixed highway traffic under moderate density conditions. As the number of diverse vehicles in the road increases, there is a sharp transition into a highly coherent state of motion characterized by all vehicles having the same average speed and a very small variance in its distribution. This state, which is analogous to the motion of a solid block, is associated with a high and stable flow, and dissapears as the vehicle density increases beyond a critical value. The effect is observed in recent measurements of highway traffic of cars and trucks in the Netherlands and should be visible in other traffic situations as well.