  The hindered diffusion model is introduced. It is a continuum model giving
the dynamics of a conserved density. Similar to the spin-facilitated models,
the kinetics are hindered by a fluctuating diffusion coefficient that decreases
as the local density approaches some geometrically constrained value where the
mobility goes to zero. The model leads in a natural way to activated dynamics
at low temperatures and high densities. In a well defined approximation the
theory is shown to be compatible with mode-coupling theory. Indeed in the
simplest form of the model we find an ergodic-nonergodic transition into a
phase that supports activated kinetics and nonergodic behavior.
