Any street, or portion thereof, made, diverted or altered under this Act shall, when completed, unless otherwise agreed, be maintained by and at the expense of the undertakers for a period of 12 months from its completion and at the expiration of that period shall be maintained by and at the expense of the highway authority.

The undertakers shall not, by reason of the obligation to maintain any street under subsection (1) above, be taken to be the street authority in relation to that street for the purposes of Part III of the Act of 1991.