According to the tender, the network ISA's mandate will be to demonstrate risk and functional safety to the satisfaction of all parties for safety-related systems including signalling, traffic management, and telecommunications.

Contractors building infrastructure and sub-systems will be expected to appoint their own ISAs, known as system ISAs, to oversee safety compliance for their respective sections of the network. This means consultants bidding for the network ISA package will not be permitted to act as assessor for system ISAs due to the potential for conflicts of interest.