California Air Resources Board

Staff modelled useful life scenarios that require trucks (or buses) older than 18 years of age or those with more than 800,000 miles and at least 13 years old to turn over to new zero emissions (ZE), new diesel combustion, and new methane combustion technology. The baseline included the impact of the following regulations: Advanced Clean Trucks (ACT), Heavy-Duty Omnibus (HD Omnibus), Heavy-Duty Inspection & Maintenance (HD I/M) with a 4x testing frequency, and Advanced Clean Fleets (ACF). Note that this baseline choice means that very substantial electrification is already assumed in this analysis; without these CARB policies favoring electric vehicles and cleaning up remaining internal combustion engines, the remaining pollution addressed in this analysis would be substantially greater and the need for electrification more acute. Of course, even with CARB policies operating to clean the fleet, turning over remaining trucks in later years is important, as this analysis shows.

This analysis considered heavy-duty Class 4-8 (Gross Vehicle Weight Rating > 14,000 lbs.) vehicles. All new California engine sales must meet the Omnibus standard beginning 2024. As such, new combustion methane and diesel vehicles are assumed to meet the Omnibus in-use standard, i.e. 0.03 g/bhp-hr (in-use threshold = 1.5). However, this assumption represents an ideal case. Preliminary results from the 200-vehicle study indicate that real-world heavy-duty emission rates can be substantially larger than their certification standard. For example, 0.02-certified methane combustion vehicles have an average in-use emission rate of 0.07 g/bhp-hr. Emissions from new combustion vehicles will be managed somewhat by regulations (e.g. in-use testing improvements through HD Omnibus), but will be larger than the in-use standard due to various vehicle operational characteristics, such as duty cycle and idling time. The summary presented in this document represents a statewide analysis and not a community level health impact analysis.