Prestressed concrete (PSC) sleepers are traditionally analysed on the basis of prescribed equivalent static loading and uniform ballast pressure distribution. However, the actual analysis requires a proper description of dynamic loading and corresponding ballast pressures, which are highly indeterminate. In this study, a rigorous dynamic analysis is carried out, by considering 3D vehicle-track interaction model. The rail-track sleepers are traditionally designed for a specified 'factor of safety' under service loads and 'load factor' under ultimate load conditions. This simplified design basis, however, does not account explicitly for the influence of the variations in strength properties of sleeper, ballast and sub-grade and uncertainties in the actual dynamic loading at the rail-seat locations. In the present study, an attempt has been made to account for the uncertainties involved, and appropriate safety factors are arrived at, using the concepts of reliability-based design.