(f)the gauge of the tramway, the rails to be used, and the mode in which, and the level at which, they shall be laid and maintained; and the adoption and application by the promoter of such improvements in the rails, and in their situation, and in the sub-structure upon which they rest, as the [Government] [Substituted 'Local Government' by the A.O. 1937.] may from time to time require;