This document discusses using a queueing model to design a lean manufacturing system based on Toyota's production system. It provides an overview of Toyota's approach of using small independent line segments separated by buffers. This allows problems to be fixed in-station to reduce rework. The document then discusses key considerations for factory designers in balancing factors like capacity, variation, buffers and costs. It provides a queueing model in an Excel file for experimenting with how changes to factors like line length, variation and over-speed impact throughput. Questions are also provided to help implement and communicate insights from the model.