  We derive the prediction of the standard model of superluminal radio sources
for the apparent transverse velocity of a radio source located at redshift z.
The apparent velocity of the source is reduced by a factor of 1 + z compared to
that of a similar nearby source. The cause of this reduction is recession of
the distant source due to the expansion of the universe. The apparent velocity
of a source can be estimated from its redshift and proper motion using the
values of the Hubble constant and the mean densities of different energy
components in the universe. We derive an expression for the velocity valid for
the currently favored cosmological model: a flat universe with a nonzero
cosmological constant.
