  We study dynamical fluctuations in overdamped diffusion processes driven by
time periodic forces. This is done by studying fluctuation functionals (rate
functions from large deviation theory), of fluctuations around the
non-equilibrium steady regime. We identify a concept called traffic. This
traffic, which was introduced in the context of non-equilibrium steady state
statistics, is extended here for time-dependent but periodic forces. We discuss
the fluctuation functionals of occupations and currents, and work out some
specific examples. The connection between these and non-equilibrium
thermodynamic potentials, their corresponding variational principles and their
Legendre transforms, are also discussed.
