  We investigate an approximation to early dynamics in relativistic heavy-ion
collisions, where after formation the partons are free streaming and around the
proper time of 1 fm/c undergo a sudden equilibration described in terms of the
Landau matching condition. We discuss physical and formal aspects of this
approach. In particular, we show that initial azimuthally asymmetric transverse
flow develops for non-central collisions as a consequence of the sudden
equilibration. Moreover, the energy-momentum tensor from the free-streaming
stage matches very smoothly to the form used in the transverse hydrodynamics,
whereas matching to isotropic hydrodynamics requires a more pronounced change
in the energy-momentum tensor. After the hydrodynamic phase statistical
hadronization is carried out with the help of THERMINATOR. The physical results
for the transverse-momentum spectra, the elliptic-flow, and the
Hanbury-Brown--Twiss correlation radii, including the ratio R_out/R_side as
well as the dependence of the radii on the azimuthal angle (azHBT), are
properly described within our approach. The agreement is equally good for a
purely hydrodynamic evolution started at an early proper time of 0.25 fm/c, or
for the free streaming started at that time, followed by the sudden
equilibration at tau ~1 fm/c and then by perfect hydrodynamics. Thus, the
inclusion of free streaming allows us to delay the start of hydrodynamics to
more realistic times of the order of 1 fm/c.
