  The majority of nearby radio-loud AGN are found in massive, old elliptical
galaxies with weak emission lines. At high redshifts,however, most known radio
AGN have strong emission lines. In this paper, we examine a subset of radio AGN
with emission lines selected from the Sloan Digital Sky Survey. The probability
for a nearby radio AGN to have emission lines is a strongly decreasing function
of galaxy mass and an increasing function of radio luminosity above 10^25 W/Hz.
Emission line and radio luminosities are correlated, but with large dispersion.
At a given radio power, AGN with small black holes have higher [OIII]
luminosities (which we interpret as higher accretion rates) than AGN with big
black holes. However, if we scale both radio and emission line luminosities by
the black hole mass, we find a correlation between normalized radio power and
accretion rate in Eddington units that is independent of black hole mass. There
is also a clear correlation between normalized radio power and the age of the
stellar population in the galaxy. Present-day AGN with the highest normalized
radio powers are confined to galaxies with small black holes. High-redshift,
high radio-luminosity AGN could be explained if big black holes were similarly
active at earlier cosmic epochs. To investigate why only a small fraction of
emission line AGN become radio loud, we create matched samples of radio-loud
and radio-quiet AGN and compare their host galaxy properties and environments.
The main difference lies in their environments; our local density estimates are
a factor 2 larger around the radio-loud AGN. We propose a scenario in which
radio-loud AGN with emission lines are located in galaxies where accretion of
both cold and hot gas can occur simultaneously. (Abridged)
