A contractual obligation to maintain infrastructure is not discharged merely by engaging a competent subcontractor; the promisor remains liable for defective subcontractor performance unless the contract expressly provides otherwise. This is a contractual, not tortious, analysis and the concept of non-delegable duty in tort is irrelevant to the contractual question. The reasonableness of a settlement with a third party is to be assessed by reference to the state of the law as known to reasonable parties at the time of settlement, not by reference to subsequent legal developments. The question whether a railway authority owes a non-delegable duty of care to users of the railway was left open.
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