Federal Clean Trucks Plan

9.3. Federal Clean Trucks Plan#

On December 20, 2022, U.S. EPA adopted “Control of Air Pollution from New Motor Vehicles: Heavy-Duty Engine and Vehicle Standards” as part of their Clean Trucks Plan (U.S. EPA, 2023). This regulation sets stricter pollutant emission standards for federally certified heavy-duty engines with gross vehicle weight rating greater than 10,000 pounds starting in 2027. Because the vast majority (over 95%) of vehicles with GVWR of 10,000 to 14,000 pounds are chassis-certified, CARB staff assumed this regulation only applies to vehicles with GVWR greater than 14,000 pounds. Over half of heavy-duty VMT in California are driven by federal-certified trucks, so they are an important source of on-road pollutant emissions. This regulation includes:

A tightened standard for the Federal Test Procedure (FTP),
A new Low Load Cycle (LLC),
Improvements to an existing heavy-duty in-use testing program,
Improvements to the durability demonstration program,
Lengthened warranty and useful life mileages.

Enhanced engine standards are expected to significantly reduce NO_x emissions, while the lengthened warranty and useful life reduce both NO_x and particulate matter (PM) emissions.

Table 9.1 lists requirements for model year 2027 and newer engines complying with Clean Trucks Plan, while Table 9.2 provides more details for off-cycle or in-use standards.

Table 9.1: Summary of Clean Trucks Plan Requirements#
Standards, Test Procedures and Elements	Engine Model Year 2027 and Newer
Federal Test Procedure (FTP)	0.035 g NO_x/bhp-hr
Low Load Cycle (LLC)	0.05 g NO_x/bhp-hr
Idling (in-use)	See off-cycle requirements in Table 9.2
In-Use Limits	See off-cycle requirements in Table 9.2
Useful Life\(^*\)	650,000/350,000/270,000/200,000 miles
Warranty\(^{*,\dagger}\)	321,000/221,000/189,000/148,000 miles

\(^*\) The mileages shown for useful life and warranty are listed in the form of HHD/MHD/LHD/HD Otto: Diesel Class 8; GVWR \(>\) 33,000 lbs. / Diesel Class 6–7; 19,500 lbs. \(<\) GVWR \(\le\) 33,000 lbs. / Diesel Class 4–5; 14,000 lbs. \(<\) GVWR \(\le\) 19,500 lbs. / HD Otto (gasoline).

\(^\dagger\) For warranty, the mileages shown are the average miles covered when considering the miles, years, and hours provisions within the proposed requirements.

Table 9.2: Clean Trucks Plan In-Use Testing/Off-Cycle Standards#
Weight Class\(^*\)	Bin\(^\dagger\)	NO_x Standard at 20 °C	NO_x Standard at 5 °C
All	1	10.4 g/hr	15.4 g/hr
LHDE	2	0.063 g/bhp-hr	0.107 g/bhp-hr
MHDE and HHDE	2	0.078 g/bhp-hr	0.122 g/bhp-hr

\(^*\) Light Heavy-Duty Engines (LHDE): GVWR 14,001–19,500 lbs.; Medium Heavy-Duty Engines (MHDE): GVWR 19,501–33,000 lbs.; Heavy Heavy-Duty Engines (HHDE): GVWR \(>\) 33,000 lbs.

\(^\dagger\) Bins 1 and 2 represent idle and non-idle operation, respectively.

The in-use or off-cycle standards ensure that real-world emissions tested with portable emissions measurement systems (PEMS) are close to the certification standard and use a 2-bin moving average window (MAW). This approach evaluates emissions data from heavy-duty engines in different time segments that are classified as idle (Bin 1) or grouped as low and medium/high load (Bin 2), ensuring they meet the in-use limits in Table 9.2. Bin 2 is calculated by the weighted average of FTP and LLC (i.e., \(0.75\times FTP + 0.25 \times LLC\)) as required by the regulation (U.S. EPA, 2023). The in-use or off-cycle standards in Clean Trucks Plan depend on the ambient temperature, with higher limits established at lower temperatures. To estimate the temperature-dependent in-use limits for engines meeting Clean Trucks Plan requirements operating in California, staff first calculated the annual average ambient temperature in EMFAC, weighted by heavy-duty vehicle miles traveled, to be 18.03 °C. Staff used the off-cycle standards interpolated to this average temperature. For Bin 1, the estimated temperature-weighted value is 12.14 g/hr; 0.078 g/bhp-hr for Bin 2 LHDE; and 0.093 g/bhp-hr for Bin 2 MHDE and HHDE.

To account for the impact of Clean Trucks Plan on heavy-duty emission rates, staff used similar methods as was used to reflect CARB’s Heavy-Duty Omnibus (Omnibus) emissions benefits in EMFAC2021. Section 4.6.4 of the EMFAC2021 Technical Documentation (CARB, 2021) provides more details. Please note that the Omnibus regulation, which has many of the same components as Clean Trucks Plan, applies to California-certified vehicles, while Clean Trucks Plan applies to Federal-certified vehicles. To estimate running exhaust emissions from Clean Trucks Plan engines, staff used the ratio of the off-cycle standard in Bin 2 at 18.03 °C to the weighted average of the FTP and LLC certification standards (0.03875 g NO_x/bhp-hr). For example, the Bin 2 ratio for MHDE and HHDE is \(0.093/0.03875 = 2.4\). This ratio was used to adjust the EMFAC base emission rates (at UDDS average speed of 18.9 mph) from the certification standard to the off-cycle emission rate limits for federal-certified trucks with engine model years 2027 and newer. Staff assumed that the speed correction factors that are used to adjust the base emission rate to other EMFAC speed bins for vehicles affected by Clean Trucks Plan are consistent with those applied to vehicles certified to 0.2 g/bhp-hr NO_x.

To estimate idle emissions rates for Clean Trucks Plan engines, staff scaled idle emission rates of 0.2 g NO_x/bhp-hr certified engines by applying the ratio of the interpolated Bin 2 emission rate of 12.4 g/hr to the model year 2010 standard (30 g/hr). The Bin 2 emission rate of 12.4 g NO_x/hr is larger than the Omnibus standard of 5.0 g/hr for engine model years 2027 and newer. Note that the idling emission rate of 2010 and newer heavy-duty engines in EMFAC depends on the season due to accessory loading (i.e., air conditioner or heater usage); the idle emission rate is 25.3 g NO_x/hr without accessory loading, but can go up to around 43 g NO_x/hr with accessory loading (CARB, 2018).