; and (II) as the Commission determines to be appropriate, promulgate comparable regulations pursuant to which the Commission may establish categorical exclusions for, and apply categorical exclusions to, qualifying projects. (ii) Transition period Until the date on which the regulations described in clause (i)(II) are promulgated by the Commission, the Commission may apply section 380.4 of title 18, Code of Federal Regulations (or a successor regulation), to qualifying projects. (10) NEPA processes and compliance (A) Purpose The purpose of this paragraph is to ensure that there is no duplication of effort or processes with respect to environmental reviews relating to the siting, construction, or modification of national interest electric transmission facilities in national interest electric transmission corridors designated by the Secretary under paragraph (2) or (5) of subsection (b). (B) Review relating to designation Unless the Secretary determines that the preparation of an environmental review document with respect to the designation of a national interest electric transmission corridor under paragraph (2) or (5) of subsection (b) is appropriate under the circumstances, the Secretary shall not be required to prepare an environmental review document in connection with the designation of a national interest electric transmission corridor under those paragraphs. (C) Effect on siting, construction, or modification of facilities (i) No review relating to designation of corridor If the Secretary has not prepared an environmental review document with respect to the designation of a national interest electric transmission corridor under paragraph (2) or (5) of subsection (b), the Commission shall prepare an environmental review document, in accordance with this subsection, for any siting, construction, or modification of a national interest electric transmission facility in that national interest electric transmission corridor. (ii) Review relating to designation of corridor If the Secretary has prepared an