  Radio relics have been discovered in many galaxy clusters. They are believed
to trace shock fronts induced by cluster mergers. Cosmological simulations
allow us to study merger shocks in detail since the intra-cluster medium is
heated by shock dissipation. Using high resolution cosmological simulations,
identifying shock fronts and applying a parametric model for the radio emission
allows us to simulate the formation of radio relics. We analyze a simulated
shock front in detail. We find a rather broad Mach number distribution. The
Mach number affects strongly the number density of relativistic electrons in
the downstream area, hence, the radio luminosity varies significantly across
the shock surface. The abundance of radio relics can be modeled with the help
of the radio power probability distribution which aims at predicting radio
relic number counts. Since the actual electron acceleration efficiency is not
known, predictions for the number counts need to be normalized by the observed
number of radio relics. For the characteristics of upcoming low frequency
surveys we find that about thousand relics are awaiting discovery.
