  We investigate the totally asymmetric simple exclusion process (TASEP) in the
presence of a bottleneck, i.e. a sequence of consecutive defect sites with
reduced hopping rate. The influence of such a bottleneck on the phase diagram
is studied by computer simulations and a novel analytical approach. We find a
clear dependence of the current and the properties of the phase diagram not
only on the length of the bottleneck, but also on its position. For bottlenecks
near the boundaries, this motivates the concept of effective boundary rates.
Furthermore the inclusion of a second, smaller bottleneck far from the first
one has no influence on the transport capacity. These results will form the
basis of an effective description of the disordered TASEP and are relevant for
the modelling of protein synthesis or intracellular transport systems where the
motion of molecular motors is hindered by immobile blocking molecules.
