Safety critical functions of the engineered railway need to perform at levels of integrity that are so high that an acceptable failure rate cannot be demonstrated through testing alone. Where such functions need to be implemented in complex programmable electronic systems certain design, build and test requirements are defined in technical standards and these are deemed to ensure that the correct level of systematic integrity is achieved. These approaches are based on assumptions around how system requirements are managed and delivered which are increasingly challenging to meet in practice. In particular the V&V lifecycle used in functional safety standards and emerging cyber security design standards is idealised. It assumes a top-down cascade of requirements for each delivery project. The approaches have become the de-facto standard internationally and are now mandated to an extent in European railway safety regulations. This paper proposes a different approach: a new lifecycle model that aligns better with the reality of the modern global supply chain and the order in which asset design and project delivery activities are actually undertaken to improve the ability to proactively manage safety.This leads to a fundamental change in the assurance philosophy to bring a simpler and more understandable approach. A framework for applying this approach is set out along with further research objectives to deliver the solution in practice.

中文翻译：

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重新定义铁路系统验证和确认：安全/安保 STAIRCASE 模型

工程铁路的安全关键功能需要以如此高的完整性水平执行，以至于仅通过测试无法证明可接受的故障率。如果需要在复杂的可编程电子系统中实现此类功能，则在技术标准中定义了某些设计、构建和测试要求，这些要求被视为确保达到正确的系统完整性水平。这些方法基于有关如何管理和交付系统需求的假设，这些假设在实践中越来越难以满足。特别是功能安全标准和新兴网络安全设计标准中使用的 V&V 生命周期是理想化的。它假设每个交付项目都有自上而下的级联需求。这些方法已成为国际上事实上的标准，现在在欧洲铁路安全法规中得到一定程度的强制。本文提出了一种不同的方法：一种新的生命周期模型，该模型更好地与现代全球供应链的现实以及实际进行资产设计和项目交付活动的顺序相一致，以提高主动管理安全的能力。这导致保证理念的根本变化，带来更简单、更易于理解的方法。制定了应用这种方法的框架以及进一步的研究目标，以在实践中提供解决方案。一种新的生命周期模型，该模型更符合现代全球供应链的现实以及实际进行资产设计和项目交付活动的顺序，以提高主动管理安全的能力。这导致保证理念发生根本性变化，以带来更简单、更易理解的方法。制定了应用这种方法的框架以及进一步的研究目标，以在实践中提供解决方案。一种新的生命周期模型，该模型更符合现代全球供应链的现实以及实际进行资产设计和项目交付活动的顺序，以提高主动管理安全的能力。这导致保证理念发生根本性变化，以带来更简单、更易理解的方法。制定了应用这种方法的框架以及进一步的研究目标，以在实践中提供解决方案。