Two forms of risk estimation are covered in this guide:
- Quantified risk estimation - estimation of the likelihood or frequency of an adverse event using numerical data on incident frequency and consequence, typically applied to national, regional or whole route assessments
- Risk rating – a form of assessment combining data and qualitative information to produce a risk rating from very low to very high, typically applied to local / small area risk assessment, such as a train station or depot.
Risk rating can be applied by use of location specific incident data and knowledge of the location. Quantified Risk Estimation for trespass may require data on the likelihood of fatal and major injuries which is less likely to be available for a single location.
Quantified Risk Estimation can require more time than qualitative risk rating and so may be preferred when assessing higher value interventions.
The time and cost of the assessment needs to be proportionate to the risk and cost of intervention. If there is evidence that a large area/system, such as a section of rural running line, is low or very low risk (for example, due to a low or very low rate of incidents, as shown in the Define and Screen section), an option is to perform a qualitative risk rating. In this case, a qualitative risk assessment of a large area or system could be proportionate to the low level of incidents, unless there is evidence to the contrary.
More information on these risk estimation methods is provided in the risk analysis web pages.