Given that signaling and safety systems are strongly affected by the rapid change in technology and subject to varying rules and regulations, most railway infrastructure operators are currently using a large number of different and partly dated interlocking systems. Therefore, priorities regarding cost- and safety effectiveness have to be assigned in an objective manner during the constant upgrading and renovation process of railway networks. The paper presents a newly developed application of risk-based decision making methodology for the necessity of specific safety functions within dated interlocking systems. Focus is kept on the assessment of specific safety functions which especially help to avoid human errors. The methodology combines a fully quantitative risk model with an absolute assessment criterion derived from a normative recommendation. The presented approach serves as a basis for the development of future decision tools and equipment standards and therefore may have a noticeable impact on the future appearance of national railway networks.