  One-dimensional asymmetric simple exclusion processes (ASEPs) which are
coupled to external reservoirs via diffusive transport are studied. These ASEPs
consist of active compartments characterized by directed movements of the
particles and diffusive compartments in which the particles undergo unbiased
diffusion. Phase diagrams are obtained by a self-consistent mean field approach
and by Monte Carlo simulations. The diffusive compartments act as diffusive
bottlenecks if the velocity of the driven compartments or ASEPs is sufficiently
large. A diffusive bottleneck at the boundary of the system leads to the
absence of a maximal current phase, while a diffusive bottleneck in the
interior of the system leads to a new phase characterized by different
densities in the two active compartments adjacent to the diffusive one and to a
maximal current defined by the bottleneck.
