Threshold diffusion in a tilted washboard potential

We characterize the locked-to-running transition of a Brownian particle in a tilted washboard potential by looking at its transport properties in the vicinity of the transition threshold. At low temperatures the (normal) spatial diffusion of the particle is enhanced as a consequence of the unlocking mechanism; in the overdamped regime an analytic expression is obtained that relates the particle diffusion constant to its mobility; in the underdamped regime an unusually large diffusion constant is revealed through numerical simulation. The latter regime is analyzed in terms of multiple jump statistics.