The terms manufacture and manufacturer are used as defined in section 501 of the Act and the terms commercial medium-duty and heavy-duty on highway vehicle, fuel and work truck are used as defined in 49 U.S.C. 32901. See 49 CFR 523.2 for general definitions related to NHTSA's fuel efficiency programs.

Act means the Motor Vehicle Information and Cost Savings Act, as amended by Pub. L. 94-163 and 96-425.

Administrator means the Administrator of the National Highway Traffic Safety Administration (NHTSA) or the Administrator's delegate.

Advanced technology means vehicle technology under this fuel consumption program in §§535.6 and 535.7 and by EPA under 40 CFR 86.1819-14(d)(7), 1036.615, or 1037.615.

Alterers means a manufacturer that modifies an altered vehicle as defined in 49 CFR 567.3

Alternative fuel conversion has the meaning given for clean alternative fuel conversion in 40 CFR 85.502.

A to B testing has the meaning given in 40 CFR 1037.801.

Automated manual transmission has the meaning given in 40 CFR 1037.801.

Automatic tire inflation system has the meaning given in 40 CFR 1037.801.

Automatic transmission (AT) has the meaning given in 40 CFR 1037.801.

Auxiliary power unit has the meaning given in 40 CFR 1037.801.

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).

Axle ratio or Drive axle ratio, ka has the meaning given in 40 CFR 1037.801.

Basic vehicle frontal area has the meaning given in 40 CFR 1037.801.

Cab-complete vehicle has the meaning given in 49 CFR 523.2.

Carryover has the meaning given in 40 CFR 1037.801.

Certificate holder means the manufacturer who holds the certificate of conformity for the vehicle or engine and that assigns the model year based on the date when its manufacturing operations are completed relative to its annual model year period.

Certificate of Conformity means an approval document granted by EPA to a manufacturer that submits an application for a vehicle or engine emissions family in 40 CFR 1036.205 and 1037.205. A certificate of conformity is valid from the indicated effective date until December 31 of the model year for which it is issued. The certificate must be renewed annually for any vehicle a manufacturer continues to produce.

Certification has the meaning given in 40 CFR 1037.801.

Certified emission level has the meaning given in 40 CFR 1036.801.

Chassis-cab means the incomplete part of a vehicle that includes a frame, a completed occupant compartment and that requires only the addition of cargo-carrying, work-performing, or load-bearing components to perform its intended functions.

Chief Counsel means the NHTSA Chief Counsel, or his or her designee.

Class means relating to GVWR classes for vehicles other than trailers, as follows:

(1) Class 2b vehicles are vehicles with a gross vehicle weight rating (GVWR) ranging from 8,501 to 10,000 pounds.

(2) Class 3 through Class 8 vehicles are vehicles with a gross vehicle weight rating (GVWR) of 10,001 pounds or more as defined in 49 CFR 565.15.

Complete sister vehicle is a complete vehicle of the same configuration as a cab-complete vehicle.

Complete vehicle has the meaning given in 49 CFR part 523.

Compression-ignition (CI) means relating to a type of reciprocating, internal-combustion engine, such as a diesel engine, that is not a spark-ignition engine. Note, in accordance with 40 CFR 1036.1, gas turbine engines and other engines not meeting the definition of compression-ignition are deemed to be compression-ignition engines for complying with fuel consumption standards.

Configuration means a subclassification within a test group for passenger cars, light trucks and medium-duty passenger vehicles and heavy-duty pickup trucks and vans which is based on basic engine, engine code, transmission type and gear ratios, and final drive ratio.

Container chassis trailer has the same meaning as container chassis in 40 CFR 1037.801.

Curb weight has the meaning given in 40 CFR 86.1803.

Custom chassis vehicle means a vocational vehicle that is a motor home, school bus, refuse hauler, concrete mixer, emergency vehicle, mixed-use vehicle or other buses that are not school buses or motor coaches. These vehicle types are defined in 49 CFR 523.3. A “mixed-use vehicle” is one that meets at least one of the criteria specified in 40 CFR 1037.631(a)(1) or at least one of the criteria in 40 CFR 1037.631(a)(2), but not both.

Date of manufacture means the date on which the certifying vehicle manufacturer completes its manufacturing operations, except as follows:

(1) Where the certificate holder is an engine manufacturer that does not manufacture the complete or incomplete vehicle, the date of manufacture of the vehicle is based on the date assembly of the vehicle is completed.

(2) EPA and NHTSA may approve an alternate date of manufacture based on the date on which the certifying (or primary) vehicle manufacturer completes assembly at the place of main assembly, consistent with the provisions of 40 CFR 1037.601 and 49 CFR 567.4.

(3) A vehicle manufacturer that completes assembly of a vehicle at two or more facilities may ask to use as the month and year of manufacture, for that vehicle, the month and year in which manufacturing is completed at the place of main assembly, consistent with provisions of 49 CFR 567.4, as the model year. Note that such staged assembly is subject to the provisions of 40 CFR 1068.260(c). NHTSA's allowance of this provision is effective when EPA approves the manufacturer's certificates of conformity for these vehicles.

Day cab has the meaning given in 40 CFR 1037.801.

Drayage tractor has the meaning given in 40 CFR 1037.801.

Dual-clutch transmission (DCT) means a transmission has the meaning given in 40 CFR 1037.801.

Dual-fuel has the meaning given in 40 CFR 1037.801.

Electric vehicle has the meaning given in 40 CFR 1037.801.

Emergency vehicle means a vehicle that meets one of the criteria in 40 CFR 1037.801.

Engine family has the meaning given in 40 CFR 1036.230. Manufacturers designate families in accordance with EPA provisions and may not choose different families between the NHTSA and EPA programs.

Excluded means a vehicle or engine manufacturer or component is not required to comply with any aspects with the NHTSA fuel consumption program.

Exempted means a vehicle or engine manufacturer or component is not required to comply with certain provisions of the NHTSA fuel consumption program.

Family certification level (FCL) has the meaning given in 40 CFR 1036.801.

Family emission limit (FEL) has the meaning given in 40 CFR 1037.801.

Final drive ratio has the meaning given in 40 CFR 1037.801.

Final-stage manufacturer has the meaning given in 49 CFR 567.3 and includes secondary vehicle manufacturers as defined in 40 CFR 1037.801.

Flatbed trailer has the meaning given in 40 CFR 1037.801.

Fleet in this part means all the heavy-duty vehicles or engines within each of the regulatory sub-categories that are manufactured by a manufacturer in a particular model year and that are subject to fuel consumption standards under §535.5.

Fleet average fuel consumption is the calculated average fuel consumption performance value for a manufacturer's fleet derived from the production weighted fuel consumption values of the unique vehicle configurations within each vehicle model type that makes up that manufacturer's vehicle fleet in a given model year. In this part, the fleet average fuel consumption value is determined for each manufacturer's fleet of heavy-duty pickup trucks and vans.

Fleet average fuel consumption standard is the actual average fuel consumption standard for a manufacturer's fleet derived from the production weighted fuel consumption standards of each unique vehicle configuration, based on payload, tow capacity and drive configuration (2, 4 or all-wheel drive), of the model types that makes up that manufacturer's vehicle fleet in a given model year. In this part, the fleet average fuel consumption standard is determined for each manufacturer's fleet of heavy-duty pickup trucks and vans.

Fuel cell means an electrochemical cell that produces electricity via the non-combustion reaction of a consumable fuel, typically hydrogen.

Fuel cell electric vehicle means a motor vehicle propelled solely by an electric motor where energy for the motor is supplied by a fuel cell.

Fuel efficiency means the amount of work performed for each gallon of fuel consumed.

Gaseous fuel has the meaning given in 40 CFR 1037.801.

Greenhouse gas Emissions Model (GEM) has the meaning given in 40 CFR 1037.801.

Gross axle weight rating (GAWR) has the meaning given in 49 CFR 571.3.

Gross combination weight rating (GCWR) has the meaning given in 49 CFR 571.3.

Gross vehicle weight rating (GVWR) has the meaning given in 49 CFR 571.3.

Good engineering judgment has the meaning given in 40 CFR 1068.30. See 40 CFR 1068.5 for the administrative process used to evaluate good engineering judgment.

Heavy-duty off-road vehicle means a heavy-duty vocational vehicle or vocational tractor that is intended for off-road use.

Heavy-duty vehicle has the meaning given in 49 CFR part 523.

Heavy-haul tractor has the meaning given in 40 CFR 1037.801.

Heavy heavy-duty (HHD) vehicle has the meaning given in vehicle service class.

Hybrid engine or hybrid powertrain means an engine or powertrain that includes energy storage features other than a conventional battery system or conventional flywheel. Supplemental electrical batteries and hydraulic accumulators are examples of hybrid energy storage systems. Note that certain provisions in this part treat hybrid engines and powertrains intended for vehicles that include regenerative braking different than those intended for vehicles that do not include regenerative braking.

Hybrid vehicle means a vehicle that includes energy storage features (other than a conventional battery system or conventional flywheel) in addition to an internal combustion engine or other engine using consumable chemical fuel. Supplemental electrical batteries and hydraulic accumulators are examples of hybrid energy storage systems Note that certain provisions in this part treat hybrid vehicles that include regenerative braking different than those that do not include regenerative braking.

Idle operation has the meaning given in 40 CFR 1037.801.

Incomplete vehicle has the meaning given in 49 CFR part 523. For the purpose of this regulation, a manufacturer may request EPA and NHTSA to allow the certification of a vehicle as an incomplete vehicle if it manufactures the engine and sells the unassembled chassis components, provided it does not produce and sell the body components necessary to complete the vehicle.

Innovative technology means technology certified under §535.7 and by EPA under 40 CFR 86.1819-14(d)(13), 1036.610, and 1037.610 in the Phase 1 program.

Intermediate manufacturer has the meaning given in 49 CFR 567.3.

Light heavy-duty (LHD) vehicle has the meaning given in vehicle service class.

Liquefied petroleum gas (LPG) has the meaning given in 40 CFR 1036.801.

Low rolling resistance tire means a tire on a vocational vehicle with a tire rolling resistance level (TRRL) of 7.7 kg/metric ton or lower, a steer tire on a tractor with a TRRL of 7.7 kg/metric ton or lower, or a drive tire on a tractor with a TRRL of 8.1 kg/metric ton or lower.

Manual transmission (MT) has the meaning given in 40 CFR 1037.801.

Medium heavy-duty (MHD) vehicle has the meaning given in vehicle service class.

Model type has the meaning given in 40 CFR 600.002.

Model year as it applies to vehicles means:

(1) For tractors and vocational vehicles with a date of manufacture on or after January 1, 2021, the vehicle's model year is the calendar year corresponding to the date of manufacture; however, the vehicle's model year may be designated to be the year before the calendar year corresponding to the date of manufacture if the engine's model year is also from an earlier year. Note that subparagraph (2) of this definition limits the extent to which vehicle manufacturers may install engines built in earlier calendar years. Note that 40 CFR 1037.601(a)(2) limits the extent to which vehicle manufacturers may install engines built in earlier calendar years.

(2) For trailers and for Phase 1 tractors and vocational vehicles with a date of manufacture before January 1, 2021, model year means the manufacturer's annual new model production period, except as restricted under this definition. It must include January 1 of the calendar year for which the model year is named, may not begin before January 2 of the previous calendar year, and it must end by December 31 of the named calendar year. The model year may be set to match the calendar year corresponding to the date of manufacture.

(i) The manufacturer who holds the certificate of conformity for the vehicle must assign the model year based on the date when its manufacturing operations are completed relative to its annual model year period. In unusual circumstances where completion of your assembly is delayed, we may allow you to assign a model year one year earlier, provided it does not affect which regulatory requirements will apply.

(ii) Unless a vehicle is being shipped to a secondary manufacturer that will hold the certificate of conformity, the model year must be assigned prior to introduction of the vehicle into U.S. commerce. The certifying manufacturer must redesignate the model year if it does not complete its manufacturing operations within the originally identified model year. A vehicle introduced into U.S. commerce without a model year is deemed to have a model year equal to the calendar year of its introduction into U.S. commerce unless the certifying manufacturer assigns a later date.

Model year as it applies to engines means the manufacturer's annual new model production period, except as restricted under this definition. It must include January 1 of the calendar year for which the model year is named, may not begin before January 2 of the previous calendar year, and it must end by December 31 of the named calendar year. Manufacturers may not adjust model years to circumvent or delay compliance with emission standards or to avoid the obligation to certify annually.

Natural gas has the meaning given in 40 CFR 1036.801. Vehicles that use a pilot-ignited natural gas engine (which uses a small diesel fuel ignition system), are still considered natural gas vehicles.

NHTSA Enforcement means the NHTSA Associate Administrator for Enforcement, or his or her designee.

Neutral coasting has the meaning given in 40 CFR 1037.801.

Off-cycle technology means technology certified under §535.7 and by EPA under 40 CFR 86.1819-14(d)(13), 1036.610, and 1037.610 in the Phase 2 program.

Party means the person alleged to have committed a violation of §535.9, and includes manufacturers of vehicles and manufacturers of engines.

Payload means in this part the resultant of subtracting the curb weight from the gross vehicle weight rating.

Petroleum has the meaning given in 40 CFR 1037.801.

Phase 1 means the joint NHTSA and EPA program established in 2011 for fuel efficiency standards and greenhouse gas emissions standards regulating medium- and heavy-duty engines and vehicles. See §535.5 for the specific model years that standards apply to vehicles and engines.

Phase 2 means the joint NHTSA and EPA program established in 2016 for fuel efficiency standards and greenhouse gas emissions standards regulating medium- and heavy-duty vehicles including trailers, and engines. See §535.5 for the specific model years that standards apply to vehicles and engines.

Pickup truck has the meaning given in 49 CFR part 523.

Plug-in hybrid electric vehicle (PHEV) means a hybrid electric vehicle that has the capability to charge the battery or batteries used for vehicle propulsion from an off-vehicle electric source, such that the off-vehicle source cannot be connected to the vehicle while the vehicle is in motion.

Power take-off (PTO) means a secondary engine shaft or other system on a vehicle that provides substantial auxiliary power for purposes unrelated to vehicle propulsion or normal vehicle accessories such as air conditioning, power steering, and basic electrical accessories. A typical PTO uses a secondary shaft on the engine to transmit power to a hydraulic pump that powers auxiliary equipment such as a boom on a bucket truck.

Powertrain family has the meaning given in 40 CFR 1037.231. Manufacturers choosing to perform powertrain testing as specified in 40 CFR 1037.550, divide product lines into powertrain families that are expected to have similar fuel consumptions and CO2 emission characteristics throughout the useful life.

Preliminary approval means approval granted by an authorized EPA representative prior to submission of an application for certification, consistent with the provisions of 40 CFR 1037.210. For requirements involving NHTSA, EPA will ensure decisions are jointly made and will convey the decision to the manufacturer.

Primary intended service class has the same meaning for engines as specified in 40 CFR 1036.140. Manufacturers must identify a single primary intended service class for each engine family that best describes vehicles for which it designs and markets the engine, as follows:

(1) Divide compression-ignition engines into primary intended service classes based on the following engine and vehicle characteristics:

(i) Light heavy-duty “LHD” engines usually are not designed for rebuild and do not have cylinder liners. Vehicle body types in this group might include any heavy-duty vehicle built from a light-duty truck chassis, van trucks, multi-stop vans, and some straight trucks with a single rear axle. Typical applications would include personal transportation, light-load commercial delivery, passenger service, agriculture, and construction. The GVWR of these vehicles is normally below 19,500 pounds.

(ii) Medium heavy-duty “MHD” engines may be designed for rebuild and may have cylinderliners. Vehicle body types in this group would typically include school buses, straight trucks with single rear axles, city tractors, and a variety of special purpose vehicles such as small dump trucks, and refuse trucks. Typical applications would include commercial short haul and intra-city delivery and pickup. Engines in this group are normally used in vehicles whose GVWR ranges from 19,500 to 33,000 pounds.

(iii) Heavy heavy-duty “HHD” engines are designed for multiple rebuilds and have cylinder liners. Vehicles in this group are normally tractors, trucks, straight trucks with dual rear axles, and buses used in inter-city, long-haul applications. These vehicles normally exceed 33,000 pounds GVWR.

(2) Divide spark-ignition engines into primary intended service classes as follows:

(i) Spark-ignition engines that are best characterized by paragraph (1)(i) or (ii) of this definition are in a separate “spark-ignition” primary intended service class.

(ii) Spark-ignition engines that are best characterized by paragraph (1)(iii) of this definition share a primary intended service class with compression-ignition heavy heavy-duty engines. Gasoline-fueled engines are presumed not to be characterized by paragraph (1)(iii) of this definition; for example, vehicle manufacturers may install some number of gasoline-fueled engines in Class 8 trucks without causing the engine manufacturer to consider those to be heavy heavy-duty engines.

(iii) References to “spark-ignition standards” in this part relate only to the spark-ignition engines identified in paragraph (b)(1) of this section. References to “compression-ignition standards” in this part relate to compression-ignition engines, to spark-ignition engines optionally certified to standards that apply to compression-ignition engines, and to all engines identified under paragraph (b)(2) of this section as heavy heavy-duty engines.

Rechargeable Energy Storage System (RESS) means the component(s) of a hybrid engine or vehicle that store recovered energy for later use, such as the battery system in a electric hybrid vehicle.

Refuse hauler has the meaning given in 40 CFR 1037.801.

Regional has the meaning relating to the Regional duty cycle as specified in 40 CFR 1037.510.

Regulatory category means each of the four types of heavy-duty vehicles defined in 49 CFR 523.6 and the heavy-duty engines used in these heavy-duty vehicles.

Regulatory subcategory means the sub-groups in each regulatory category to which mandatory fuel consumption standards and requirements apply as specified in 40 CFR 1036.230 and 1037.230 and are defined as follows:

(1) Heavy-duty pick-up trucks and vans.

(2) Vocational vehicle subcategories have 18 separate vehicle service classes as shown in Tables 1 and 2 below and include vocational tractors. Table 1 includes vehicles complying with Phase 1 standards. Phase 2 vehicles are included in Table 2 which have separate subcategories to account for engine characteristics, GVWR, and the selection of duty cycle for vocational vehicles as specified in 40 CFR 1037.510; vehicles may additionally fall into one of the subcategories defined by the custom-chassis standards in §535.5(b)(6) and 40 1037.105(h). Manufacturers using the alternate standards in §535.5(b)(6) and 40 CFR 1037.105(h) should treat each vehicle type as a separate vehicle subcategory.

(3) Tractor subcategories are shown in Table 3 below for Phase 1 and 2. Table 3 includes 10 separate subcategories for tractors complying with Phase 1 and 2 standards. The heavy-haul tractor subcategory only applies for Phase 2.

(4) Trailer subcategories are shown in Table 4 of this section for the Phase 2 program. Trailers do not comply under the Phase 1 program. Table 4 includes 10 separate subcategories for trailers, which are only subject to Phase 2 only standards.

(5) Engine subcategories are shown for each primary intended service class in Table 5 below. Table 5 includes 6 separate subcategories for engines which are the same for Phase 1 and 2 standards.

Revoke has the same meaning given in 40 CFR 1068.30.

Roof height means the maximum height of a vehicle (rounded to the nearest inch), excluding narrow accessories such as exhaust pipes and antennas, but including any wide accessories such as roof fairings. Measure roof height of the vehicle configured to have its maximum height that will occur during actual use, with properly inflated tires and no driver, passengers, or cargo onboard. Determine the base roof height on fully inflated tires having a static loaded radius equal to the arithmetic mean of the largest and smallest static loaded radius of tires a manufacturer offers or a standard tire EPA approves. If a vehicle is equipped with an adjustable roof fairing, measure the roof height with the fairing in its lowest setting. Once the maximum height is determined, roof heights are divided into the following categories:

(1) Low-roof means a vehicle with a roof height of 120 inches or less.

(2) Mid-roof means a vehicle with a roof height between 121 and 147 inches.

(3) High-roof means a vehicle with a roof height of 148 inches or more.

Secondary vehicle manufacturer has the same meaning as final-stage manufacturer in 49 CFR part 567.

Service class group means a group of engine and vehicle averaging sets defined as follows:

(1) Spark-ignition engines, light heavy-duty compression-ignition engines, light heavy-duty vocational vehicles and heavy-duty pickup trucks and vans.

(2) Medium heavy-duty compression-ignition engines and medium heavy-duty vocational vehicles and tractors.

(3) Heavy heavy-duty compression-ignition engines and heavy heavy-duty vocational vehicles and tractors.

Sleeper cab means a type of truck cab that has a compartment behind the driver's seat intended to be used by the driver for sleeping. This includes both cabs accessible from the driver's compartment and those accessible from outside the vehicle.

Small business manufacturer means a manufacturer meeting the criteria specified in 13 CFR 121.201. For manufacturers owned by a parent company, the employee and revenue limits apply to the total number employees and total revenue of the parent company and all its subsidiaries.

Spark-ignition (SI) means relating to a gasoline-fueled engine or any other type of engine with a spark plug (or other sparking device) and with operating characteristics significantly similar to the theoretical Otto combustion cycle. Spark-ignition engines usually use a throttle to regulate intake air flow to control power during normal operation. Note that some spark-ignition engines are subject to requirements that apply for compression-ignition engines as described in 40 CFR 1036.140.

Standard payload means the payload assumed for each vehicle, in tons, for modeling and calculating emission credits, as follows:

(1) For vocational vehicles:

(i) 2.85 tons for light heavy-duty vehicles.

(ii) 5.6 tons for medium heavy-duty vehicles.

(iii) 7.5 tons for heavy heavy-duty vocational vehicles.

(2) For tractors:

(i) 12.5 tons for Class 7.

(ii) 19 tons for Class 8.

(iii) 43 tons for heavy-haul tractors.

(3) For trailers:

(i) 10 tons for short box vans.

(ii) 19 tons for other trailers.

Standard tractor has the meaning given in 40 CFR 1037.501.

Standard trailer has the meaning given in 40 CFR 1037.501.

Subconfiguration means a unique combination within a vehicle configuration of equivalent test weight, road-load horsepower, and any other operational characteristics or parameters that EPA determines may significantly affect CO2 emissions within a vehicle configuration as defined in 40 CFR 600.002.

Tank trailer has the meaning given in 40 CFR 1037.801.

Test group means the multiple vehicle lines and model types that share critical emissions and fuel consumption related features and that are certified as a group by a common certificate of conformity issued by EPA and is used collectively with other test groups within an averaging set or regulatory subcategory and is used by NHTSA for determining the fleet average fuel consumption.

The agencies means the National Highway Traffic Safety Administration (NHTSA) and the Environmental Protection Agency (EPA) in this part.

Tire pressure monitoring system (TPMS) has the meaning given in section S3 of 49 CFR 571.138.

Tire rolling resistance level (TRRL) means a value with units of kg/metric ton that represents that rolling resistance of a tire configuration. TRRLs are used as inputs to the GEM model under 40 CFR 1037.520. Note that a manufacturer may assign a value higher than a measured rolling resistance of a tire configuration.

Towing capacity in this part is equal to the resultant of subtracting the gross vehicle weight rating from the gross combined weight rating.

Trade means to exchange fuel consumption credits, either as a buyer or a seller.

U.S.-directed production volume means the number of vehicle units, subject to the requirements of this part, produced by a manufacturer for which the manufacturer has a reasonable assurance that sale was or will be made to ultimate purchasers in the United States.

Useful life has the meaning given in 40 CFR 1036.801 and 1037.801.

Vehicle configuration means a unique combination of vehicle hardware and calibration (related to measured or modeled emissions) within a vehicle family as specified in 40 CFR 1037.801. Vehicles with hardware or software differences, but that have no hardware or software differences related to measured or modeled emissions or fuel consumption can be included in the same vehicle configuration. Note that vehicles with hardware or software differences related to measured or modeled emissions or fuel consumption are considered to be different configurations even if they have the same GEM inputs and FEL. Vehicles within a vehicle configuration differ only with respect to normal production variability or factors unrelated to measured or modeled emissions and fuel consumption for EPA and NHTSA.

Vehicle family has the meaning given in 40 CFR 1037.230. Manufacturers designate families in accordance with EPA provisions and may not choose different families between the NHTSA and EPA programs. If a manufacturer is certifying vehicles within a vehicle family to more than one FEL, it must subdivide its greenhouse gas and fuel consumption vehicle families into subfamilies that include vehicles with identical FELs. Note that a manufacturer may add subfamilies at any time during the model year.

Vehicle service class has the same meaning for vehicles as specified in 40 CFR 1037.140. Fuel consumption standards and other provisions of this part apply to specific vehicle service classes for tractors and vocational vehicles as follows:

(1) Phase 1 and Phase 2 tractors are divided based on GVWR into Class 7 tractors and Class 8 tractors. Where provisions apply to both tractors and vocational vehicles, Class 7 tractors are considered medium heavy-duty “MHD” vehicles and Class 8 tractors are considered heavy heavy-duty “HHD” vehicles.

(2) Phase 1 vocational vehicles are divided based on GVWR. Light heavy-duty “LHD” vehicles includes Class 2b through Class 5 vehicles; medium heavy-duty “MHD” vehicles includes Class 6 and Class 7 vehicles; and heavy heavy-duty “HHD” vehicles includes Class 8 vehicles.

(3) Phase 2 vocational vehicles with spark-ignition engines are divided based on GVWR. Light heavy-duty “LHD” vehicles includes Class 2b through Class 5 vehicles, and medium heavy-duty “MHD” vehicles includes Class 6 through Class 8 vehicles.

(4) Phase 2 vocational vehicles with compression-ignition engines are divided as follows:

(i) Class 2b through Class 5 vehicles are considered light heavy-duty “LHD” vehicles.

(ii) Class 6 through 8 vehicles are considered heavy heavy-duty “HHD” vehicles if the installed engine's primary intended service class is heavy heavy-duty (see 40 CFR 1036.140). All other Class 6 through Class 8 vehicles are considered medium heavy-duty “MHD” vehicles.

(5) In certain circumstances, manufacturers may certify vehicles to standards that apply for a different vehicle service class such as allowed in §535.5(b)(6) and (c)(7). If manufacturers optionally certify vehicles to different standards, those vehicles are subject to all the regulatory requirements as if the standards were mandatory.

Vehicle subfamily or subfamily means a subset of a vehicle family including vehicles subject to the same FEL(s).

Vocational tractor has the meaning given in 40 CFR 1037.801.

Zero emissions vehicle means an electric vehicle or a fuel cell vehicle.