12.—(1) This Article has effect where, whether before, on or after the commencement date—
(a)the carriageway of a road has been altered after the road has been open to public traffic;
(b)any public works other than a road have been reconstructed, extended or otherwise altered after they have been first used; or
(c)there has been a change of use in respect of any public works other than a road or aerodrome.
(2) If and so far as a claim in respect of the road or other public works relates to depreciation that would not have been caused but for the alterations or change of use, this Part shall, subject to paragraph (3), have effect in relation to the claim as if the relevant date (instead of being the date specified in Article 4(9)) were—
(a)the date on which the road was first open to public traffic after completion of the alterations to the carriageway;
(b)the date on which the other public works were first used after completion of the alterations; or
(c)the date of the change of use,
as the case may be.
(3) Paragraph (2) shall not by virtue of any alterations to an aerodrome apply to a claim in respect of physical factors caused by aircraft unless the alterations are runway or apron alterations.
(4) Where a claim relates to such depreciation as is mentioned in paragraph (2) the notice of claim shall specify, in addition to the matters mentioned in Article 6, the alterations or change of use alleged to give rise to the depreciation; and if and so far as the claim relates to such depreciation—
(a)Article 9 shall have effect as if the increase in value to be taken into account were any increase that would not have been caused but for the alterations or change of use in question;
(b)paragraph (1) of Article 11 shall not preclude the payment of compensation unless the previous claim was in respect of depreciation that would not have been caused but for the same alterations or change of use, and paragraph (2) of that Article shall not preclude the payment of compensation unless the works for which the land was acquired were works resulting from the alteration, or works used for the purpose, to which the claim relates.
(5) For the purposes of this Article the carriageway of a road is altered if, and only if—
(a)the location, width or level of the carriageway is altered (otherwise than by re-surfacing); or
(b)an additional carriageway is provided for the road beside, above or below an existing one;
and the reference in paragraph (2) to depreciation that would not have been caused but for alterations to the carriageway of a road is a reference to such depreciation by physical factors which are caused by the use of, and the source of which is situated on, the length of carriageway which has been altered as mentioned in sub-paragraph ( a) or, as the case may be, the additional carriageway and the corresponding length of the existing one mentioned in paragraph ( b).
(6) In this Article “runway or apron alterations” means—
(a)the construction of a new runway, the major re-alignment of an existing runway or the extension or strengthening of an existing runway; or
(b)a substantial addition to, or alteration of, a taxiway or apron, being an addition or alteration whose purpose or main purpose is the provision of facilities for a greater number of aircraft.
(7) For the avoidance of doubt it is hereby declared that references in this Article to a change of use do not include references to the intensification of an existing use.