Proposal to amend the General Guidelines for United Nations regulatory procedures and transitional provisions. The document establishes transitional provisions for vehicles, vehicle systems and installation of equipment and parts in new vehicles, including provisions applicable to all series of amendments and specific provisions for the XX series of amendments. Contracting Parties may grant type approvals according to any preceding series and shall continue to grant extensions of existing approvals. As from the official date of entry into force of the XX series, no Contracting Party shall refuse to grant or accept type approvals under the XX series. As from 1 September Date (b), Contracting Parties shall not be obliged to accept type approvals to any preceding series first issued after that date. Until 1 September Date ©, Contracting Parties shall accept type approvals to the XX-1 series first issued before 1 September Date (b). As from 1 September Date ©, Contracting Parties shall not be obliged to accept type approvals issued to any preceding series, subject to special cases permitting continued acceptance of certain equipment/parts or vehicles/vehicle systems.