In fail-safe computer systems, such as railway signaling systems, the outputs directly drive some vital units. Once they happen in error, there will be some injuries, even losses or damages. In order to improve the reliability and safety of fail-safe computer systems, in this paper, we innovatively design and implement two kinds of 2-out-of-3 voters: the dynamic voter and the static voter. The former achieves the voting function mainly with pulse demodulation circuit, and the latter realizes it mainly with four solid state relays. Furthermore, we analyze their performances with Markov model. The dynamic voter is hazard-free, and the reliability of the dynamic voter is 376 years. For so few components, the static voter is of amazing reliability with 875 years. In addition, with the help of loopback detection, it satisfies safety integrity level 4. At last, we analyze and discuss some applications of the two voters in railway signaling systems, and make suggestions on application choice.

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Automatic Train Protection (ATP) system is a safetycritical system; it is widely used to ensure trains running safely. During its development lifecycle, there are many safety problems which are derived from the requirements. In order to make descriptions of the requirements accurate and consistent, we introduce requirement models in the development lifecycle. The requirement models are built based on the modified state machine with text descriptions and the introduction of SuperState. In these models, the limitations of transitions are well defined and the complexity of the models can be reduced effectively. With this approach, the requirement of train localization function of ATP system is described clearly and strictly. Besides, this requirement model is easy to understand and read for developers.