Abstract - During twenty years of applications, computer railway interlocking systems have offered many advantages, but they have not fully satisfied expectations. This paper gives a summary of possible areas of improvement that have been observed and proposals to resolve many of them. The solutions are presented in the form of a Computer Interlocking System (CIS) which could become a standard system, independent of track layout and  country of application. The main contribution is conversion of the operational, functional and safety requirements of an interlocking system into general interlocking software. There is also a new way of presenting a control table which can be entered as a simple data file and control table conversion to the interlocking functions suitable for computer application. An advanced method of screen design showing the layout of a railway station is proposed as well.

 Keywords - Computer system, real time control, fault-tolerance, railway signalling, interlocking system, afety critical software, safety analyses, control table.