In closed production lines, each part is placed on a carrier at the input of the first machine and is removed from the carrier at the output of the last machine. The first machine is starved if no carriers are available, and the last machine is blocked if the empty carrier buffer is full. The number of carriers in the system is S and the capacity of the empty carrier buffer is N0. Under the assumption that the machines obey the Bernoulli reliability model, this paper provides methods for determining if a pair (N0, S) impedes the open line performance and, if it does, develops techniques for improvement with respect to S and N0. In addition, bottlenecks in closed lines are discussed, and an approach to selecting the smallest N0 and S, which result in no impediment, is described.