Fundamental Limitations of Basic Dangerous Failure Models for Functional Safety Assessment in Train Control Systems

The article examines the widespread practice of using the exponential distribution law for modeling hazardous failures in risk assessment of railway traffic control systems. It outlines key physical signs of aging in components of railway automation systems, which can lead to significant errors when exponential models are applied to calculate the normative indicators of functional safety. It is demonstrated that in real systems with alternative failure distributions— particularly under long-term operation (over 10 years)—such simplified calculations result in multiple misestimations of functional safety, ultimately leading to unacceptable reductions in railway traffic safety. To justify functional safety, the article recommends the use of other hazardous failure distribution laws or, during the commissioning phase, the inclusion of actual increases in failure intensity caused by aging under harsh operating conditions typical for railway automation systems.