The Board may designate one or more lanes of any highway, including lanes that may previously have been designated HOV lanes under § 33.2-501, in the Interstate System, primary state highway system, or National Highway System, or any portion thereof, as HOT lanes. In making HOT lanes designations, the Board shall also specify the high-occupancy requirement and conditions for use of such HOT lanes or may authorize the Commissioner of Highways to make such determination consistent with the terms of a comprehensive agreement executed pursuant to § 33.2-1808. The high-occupancy requirement for a HOT lanes facility constructed or operated as a result of the Public-Private Transportation Act (§ 33.2-1800 et seq.) shall not be less than three.