  Recent applications of a new methodology to measure fundamental traffic
relations on freeways shows that many of the critical parameters of the
flow-density and speed-spacing diagrams depend on vehicle length. In response
to this fact, we present in this work a generalization of the Prigogine-Herman
traffic equation for aggressive drivers which takes into account the fact that
vehicles are not point-like objects but have an effective length. Our approach
is similar to that introduced by Enskog for dense gases and provides the
construction of fundamental diagrams which are in excellent agreement with
empirical traffic data.
