15.—(1) Excluded traffic is hereby authorised to use a motorway on the occasions or in the emergencies and to the extent specified in the following provisions of this paragraph, that is to say—
(a)traffic of Classes III or IV may use a motorway for the maintenance, repair, cleaning or clearance of any part of a motorway or for the erection, laying, placing, maintenance, testing, alteration, repair or removal of any structure, works or apparatus in, on, under or over any part of a motorway;
(b)pedestrians may use a motorway—
(i)when it is necessary for them to do so as a result of an accident or emergency or of a vehicle being at rest on a motorway in any of the circumstances specified in paragraph (2) of Regulation 7, or
(ii)in any of the circumstances specified in sub-paragraphs (b), (d), (e) or (f) of paragraph (1) of Regulation 16.
(2) The Secretary of State may authorise the use of a motorway by any excluded traffic on occasion or in emergency or for the purpose of enabling such traffic to cross a motorway or to secure access to premises abutting on or adjacent to a motorway.
(3) Where by reason of any emergency the use of any road (not being a motorway) by any excluded traffic is rendered impossible or unsuitable the Chief Officer of Police of the police area in which a motorway or any part of a motorway is situated, or any officer of or above the rank of superintendent authorised in that behalf by that Chief Officer, may—
(a)authorise any excluded traffic to use that motorway or that part of a motorway as an alternative road for the period during which the use of the other road by such traffic continues to be impossible or unsuitable, and
(b)relax any prohibition or restriction imposed by these Regulations in so far as he considers it necessary to do so in connection with the use of that motorway or that part of a motorway by excluded traffic in pursuance of any such authorisation as aforesaid.