Averaging set means, a set of engines or vehicles in which fuel consumption credits may be exchanged. Credits generated by one engine or vehicle family may only be used by other respective engine or vehicle families in the same averaging set as specified in 535.7 . Note that an averaging set may comprise more than one regulatory subcategory. The averaging sets for this HD program are defined as follows:
(1) Heavy-duty pickup trucks and vans.
(2) Light heavy-duty (LHD) vehicles.
(3) Medium heavy-duty (MHD) vehicles.
(4) Heavy heavy-duty (HHD) vehicles.
(5) Light heavy-duty engines subject to compression-ignition standards.
(6) Medium heavy-duty engines subject to compression-ignition standards.
(7) Heavy heavy-duty engines subject to compression-ignition standards.
(8) Engines subject to spark-ignition standards.
(9) Long trailers.
(10) Short trailers.
(11) Vehicle types certifying to optional custom chassis standards as specified in § 535.5(b)(6) form separate averaging sets for each vehicle type as specified in § 535.7(c).