The fluid-dynamic traffic model of Kerner and Konhäuser [Phys. Rev. E 48, 2335 (1993); 50, 54 (1994)] is extended by an equation for the vehicles’ velocity variance. It is able to describe the observed increase of velocity variance immediately before a traffic jam develops. Another modification takes into account the finite amount of space that each vehicle needs. As a consequence, the improved traffic model does not produce densities that exceed the maximum vehicle density or negative velocities, like former models did.

• Received 21 March 1994

DOI:https://doi.org/10.1103/PhysRevE.51.3164