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Estimated cost of diesel emissions-control technology to meet the future California low NOx standards in 2024 and 2027

The California Air Resources Board (CARB) is developing new regulations to address disparities in real-world and certified NOx emissions from heavy-duty diesel engines. Key changes include a phased-in NOx emission targets of 90% below current limits and the adoption of low-load cycle (LLC) to supplement the traditional federal test protocol (FTP) and ensure NOx emissions compliance under urban low-speed operating conditions. The board also proposed increasing the useful life or durability requirements to better reflect HDV operating life in the United States and ensure long-term real-world emissions control. The analysis estimates the cost of the technology required to meet CARB’s envisioned regulatory changes in 2024 and 2027.

The costs of meeting EPA 2010 standards in 2019 declined significantly compared with previous cost estimates. Costs of aftertreatment technology needed to meet the EPA 2010 standard have dropped by about 25%. Total direct and indirect aftertreatment manufacturing costs in 2019 are estimated in this analysis to be $2,800 for a class 6–7 HDV with a 7.0 liter engine and $4,400 for a class 8 HDV with a 13.0 liter engine.

Meeting the envisioned CARB 2024 targets would require very modest increases in technology complexity and costs. Technology changes are expected to occur in the urea dosing system of current aftertreatment system architectures. The incremental cost of achieving a 75% reduction in NOx emissions under the FTP and meeting new LLC standards is estimated to range between $100 and $1,000 for a class 6–7 vehicle with a 7.0 liter engine and between $100 and $1,100 for a 13.0 L class 8 HDV.

Meeting the envisioned CARB 2027 targets would require significant changes in current technology and costs, driven by 90% lower FTP NOx targets, low-load cycle requirements, and longer useful life mandates. The technology changes are focused on improving thermal management and increasing the aftertreatment system NOx reduction efficiency and durability. To achieve that, cylinder deactivation and EGR bypass would be added to future engines. Aftertreatment changes would include the addition of a close-coupled SCR and changes to the urea dosing system. Higher useful life would be addressed with changes to catalyst volume and wash coat formulations, and sensor replacement. For class 6–7 HDVs with 7.0 L engines, this would result in additional $1,800 – $2,600 of total emission control costs compared with systems meeting the EPA 2010 standards in 2027. For class 8 HDVs with 13.0 L engines we estimate an increment in total cost ranging from $2,200 to $3,200 compared with systems meeting the EPA 2010 standards in 2027.

Table ES-1. Incremental total cost of the proposed 2024 CARB standards, as compared with EPA 2010 standards in 2024 (in 2019 U.S. dollars).
Table ES-2. Incremental cost of the proposed 2027 CARB standards, as compared with EPA 2010 standards in 2027 (in 2019 U.S. dollars).