Section 1037.140 - Classifying vehicles and determining vehicle parameters(a) Where applicable, a vehicle's roof height and a trailer's length are determined from nominal design specifications, as provided in this section. Specify design values for roof height and trailer length to the nearest inch.(b) 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 you offer or a standard tire we approve.(c) Base a standard trailer's length on the outer dimensions of the load-carrying structure. Do not include aerodynamic devices or HVAC units.(d) The nominal design specifications must be within the range of the actual values from production vehicles considering normal production variability. In the case of roof height, use the mean tire radius specified in paragraph (b) of this section. If after production begins it is determined that your nominal design specifications do not represent production vehicles, we may require you to amend your application for certification under § 1037.225 .(e) If your vehicle is equipped with an adjustable roof fairing, measure the roof height with the fairing in its lowest setting.(f) For any provisions in this part that depend on the number of axles on a vehicle, include lift axles or any other installed axles that can be used to carry the vehicle's weight while in motion.(g) The standards and other provisions of this part apply to specific vehicle service classes as follows:(1) Tractors are divided based on GVWR into Class 7 tractors and Class 8 tractors. Where provisions of this part apply to both tractors and vocational vehicles, Class 7 tractors are considered "Medium HDV" and Class 8 tractors are considered "Heavy HDV". This paragraph (g)(1) applies for hybrid and non-hybrid vehicles.(2) Phase 1 vocational vehicles are divided based on GVWR. "Light HDV" includes Class 2b through Class 5 vehicles; "Medium HDV" includes Class 6 and Class 7 vehicles; and "Heavy HDV" includes Class 8 vehicles.(3) Phase 2 and later vocational vehicles propelled by engines subject to the spark-ignition standards of 40 CFR part 1036 are divided as follows: (i) Class 2b through Class 5 vehicles are considered "Light HDV".(ii) Class 6 through Class 8 vehicles are considered "Medium HDV".(4) Phase 2 and later vocational vehicles propelled by engines subject to the compression-ignition standards in 40 CFR part 1036 are divided as follows:(i) Class 2b through Class 5 vehicles are considered "Light HDV".(ii) Class 6 through 8 vehicles are considered "Heavy HDV" if the installed engine's primary intended service class is Heavy HDE (see 40 CFR 1036.140 ), except that Class 8 hybrid vehicles are considered "Heavy HDV" regardless of the engine's primary intended service class.(iii) All other Class 6 through Class 8 vehicles are considered "Medium HDV".(5) Heavy-duty vehicles with no installed propulsion engine, such as battery electric vehicles, are divided as follows: (i) Class 2b through Class 5 vehicles are considered "Light HDV".(ii) Class 6 and 7 vehicles are considered "Medium HDV".(iii) Class 8 vehicles are considered "Heavy HDV".(6) In certain circumstances, you may certify vehicles to standards that apply for a different vehicle service class. For example, see §§ 1037.105(g) and 1037.106(f) . If you optionally certify vehicles to different standards, those vehicles are subject to all the regulatory requirements as if the standards were mandatory.(7) Vehicles meeting the custom-chassis standards of § 1037.105(h)(1) are subject to the following vehicle service classes instead of the other provisions in this section:(i) School buses and motor homes are considered "Medium HDV".(ii) All other custom-chassis are considered "Heavy HDV".(h) Use good engineering judgment to identify the intended regulatory subcategory (Urban, Multi-Purpose, or Regional) for each of your vocational vehicle configurations based on the expected use of the vehicles. 81 FR 74048 , Oct. 25, 2016, as amended at 86 FR 34460 , June 29, 2021; 88 FR 4638 , Jan. 24, 2023; 89 FR 29772 , Apr. 22, 2024 88 FR 4638 , 3/27/2023; 89 FR 29772 , 6/21/2024