Following the integrated approach for the planning of a (sufficiently) safe tunnel system design and operation of a tunnel has to comply with minimum safety requirements. Further, alternative or additional safety measures may be required for various reasons, like for instance:
The decision whether or not additional safety measures are required, can be based on a prescriptive as well as a risk-based approach
In general, safety measures can be grouped into 4 categories, according to their mode of action and their main effects on risk:
Measures may concern tunnel structure or tunnel equipment, as well as procedures for tunnel operation or emergency response. If the transport of dangerous goods is authorized in a tunnel specific measures may be required. Any additional safety measure needs to be integrated into the existing complex safety system of a tunnel in the best possible way, taking all relevant interaction effects into account.