Compliance versus risk assessment: when have we done enough?

In the UK railway it is necessary to show that risks relating to any design solutions are as-low-as-reasonably-practicable. It is a legal requirement and in certain instances complying with a standard may be enough. However, in other circumstances we may have to perform a formal risk assessment. It seems clear that there is a continuum between the two positions but how do we know what to do and if that is enough? This article seeks to address the question. The UK risk acceptance approach, including the as-low-as-reasonably-practicable principle, is explored and the recent initiative of the common safety method is discussed. An example of a compliance safety process against standards is given using a case study based upon changes to rolling stock. A further example where risk assessment and a cost benefit analysis have been employed to support a safety argument for a non-compliant gradient is then presented, followed by concluding remarks.