This presentation describes a system for the investigation of railway interfaces that is under development within the Rail Safety and Standards Board (RSSB). This presentation describes a proactive approach on how to assess, achieve and maintain safety, integrity and performance of complex systems using a soft systems thinking approach. To use a soft system thinking approach means to focus efforts on static and dynamic interconnections (interfaces) between the elements of a complex system using a framework of tools/techniques of systems engineering, safety engineering and human factors engineering in a bottom-up manner