Safety of the railway transport has been the major concern of the railways since they exist. The security of the railway transport is a new request faced with attacks against passengers, goods or environment. A problem of safety can be due to technical failures or unintentional human behaviour. A problem of security is always due to a negative willing of human factor. The safety cause is internal and the security cause is external to the railway process. In this paper we have presented an

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... ch for quantitative assessment of security attributes for an railway system. A state transition model that describes the dynamic behavior of such a system is used as a basis for developing a stochastic model. This is a generic model that enables the study of different impacts of a human-operator unintentional errors and intentional security attacks. Several general probability distribution functions can be used to describe the attacker behavior and t solve the proposed Semi Markov Model for safety and security related attributes.