Ensuring the system safety at all times is most important in railway systems where small failures may result in a large number of casualties and property loss. Although there are various design methods, safety precautions, and recommendations of the railway-related safety standards, sometimes the occurrence of accidents cannot be prevented. In this paper, according to the recommendations of the railway-related safety standards, an interlocking system architecture, which consists of two controllers and a coordinator, for a fixed-block railway signaling system is studied. Based on the Petri net models of railway field components, decision-making strategies including fault diagnosis are presented. (c) 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.