  Based on simulations with the ``intelligent driver model'', a microscopic
traffic model, we explain the recently discovered transition from free over
``synchronized'' traffic to stop-and-go patterns [B. S. Kerner, Phys. Rev.
Lett. 81, 3797 (1998)]. We obtain a nearly quantitative agreement with
empirical findings such as the ``pinch effect'', the flow-density diagram, the
emergence of stop-and-go waves from nonhomogeneous congested traffic, and the
dimensions of their wavelength.
