Historically, railroad signals have been, for many modelers, one of the more challenging “aspects” to incorporate on a layout for a wide variety of reasons. Regardless of size, complexity, era, or level of sophistication desired, there are very few model railroads (or model railroaders) that would not benefit from adding at least some part of this very important operation of the prototype. This clinic continues the series (Parts 1 through 4 covered Signaling Definitions, Basic Fixed and Non-Fixed Signal Operation, Routing and Interlocking, and Modular Approaches) and expands the use of Signal Topology Elements to model localized fixed tower operation as well as introduce “Rule 261” and Centralized Traffic Control concepts.