  Starting from the instability diagram of a traffic flow model, we derive
conditions for the occurrence of congested traffic states, their appearance,
their spreading in space and time, and the related increase in travel times. We
discuss the terminology of traffic phases and give empirical evidence for the
existence of a phase diagram of traffic states. In contrast to previously
presented phase diagrams, it is shown that "widening synchronized patterns" are
possible, if the maximum flow is located inside of a metastable density regime.
Moreover, for various kinds of traffic models with different instability
diagrams it is discussed, how the related phase diagrams are expected to
approximately look like. Apart from this, it is pointed out that combinations
of on- and off-ramps create different patterns than a single, isolated on-ramp.
