  In this paper we constrain the evolution in the comoving space density for
low-luminosity (typically FRI) radio sources as a function of cosmic epoch by
matching deep radio surveys (WENSS, FIRST and NVSS) with the Sloan Digital Sky
Survey (SDSS). This results in 1014 matched radio sources covering an effective
area of 0.217 sr, 686 with L(325 MHz) < 10^25 W/Hz/sr, which is an order of
magnitude larger than any previous study at these luminosities. Using the
non-parametric V/Vmax test we show that low-luminosity radio sources evolve
differently to their more powerful, predominantly FRII, counterparts. Indeed,
we find that the lower luminosity population is consistent with a constant
comoving space density with redshift, as opposed to the strong positive
evolution for the more powerful sources.
