  Hydrodynamics is applied to describe the dynamics of relativistic heavy-ion
collisions. The focus of the present study is the influence of a possible
(phase) transition to the quark-gluon plasma in the nuclear matter equation of
state on collective observables, such as the lifetime of the system and the
transverse directed flow of matter. It is shown that such a transition leads to
a softening of the equation of state, and consequently to a time-delayed
expansion which is in principle observable via two-particle correlation
functions. Moreover, the delayed expansion leads to a local minimum in the
excitation function of transverse directed flow around AGS energies.
