CARB’s Advanced Clean Fleet (ACF) regulation is a hot topic these days. Unlike the Advanced Clean Truck regulation – that applies to vehicle manufacturers – the new Fleet order applies to fleet operators. After more than three years in the making, the Final ACF Regulation Order was adopted on April 28, of 2023.  In a nutshell, the new regulation requires that fleet managers opt for zero emission vehicles (“ZEVs”, either electric or hydrogen powered) when adding or replacing vehicles, beginning as early as 2024. This article focuses on portions of the order (Appendix A-1)[1] that apply to state and local agencies.

One of the central challenges of the new regulation is that it applies to vehicles with a gross weight rating greater than 8,500 pounds i.e., Class 2b and above. Why is this challenge? Original Equipment Manufacturer (OEM) offerings in the middle and higher weight classes are relatively few. As of early 2023, there’s roughly 2,000 medium and heavy duty ZEVs – in total – on California roads, out of roughly 30.5 million motor vehicles registered in the state. And less than 500 of those ZEVs are configured to meet the operating requirements for many medium and heavy duty vehicle fleet operators. Adding to the challenge is the fact that integrating ancillary equipment like booms, buckets, pumps, vacuum motors and dump-beds – that normally involve mechanical integration with vehicle engines – involve methods that are not yet familiar to most upfitters (i.e., engine mounted hydraulics are clearly an entirely different world than high voltage power electronics). OEMs and upfitters will “get there”, but it will take time and 2024 is right around the corner.

CARB recognizes that it will take time for supply to line up with demand. And as such, CARB has included several exception categories in the ACF regulation. This is in keeping with one tenet of the Executive Order that lead to the development of the ACF regulation.

Executive Order (EO) N‑79‑20 states that, It shall be a…goal of the State that 100 percent of medium- and heavy-duty vehicles in the State be zero-emission by 2045 for all operations where feasible…” [emphasis added]

According to California Public Resources Code, DIVISION 13 – ENVIRONMENTAL QUALITY, CHAPTER 2.5 – Definitions, Section 21061.1

“Feasible” means capable of being accomplished in a successful manner within a reasonable period of time, taking into account economic, environmental, social, and technological factors.

CARB’s new ACF provides for the following exceptions:

Daily Usage: This exemption is reserved for cases where no new electric vehicle is available that can meet demonstrated daily usage needs.  In the regulation, CARB describes several restrictions on use of this type of exemption.  To begin with, CARB reserves this exception for fleets that are already comprised of at least ten percent ZEVs or “near-zero-emission vehicles” (NZEVs), which are essentially plug-in hybrids.  There are additional exception-limitations for Class 7-8 tractors and buses relating to traction-pack battery capacity. And for Class 4-6 Battery Electric Vehicles – often found in public agency fleets – CARB indicates that they are not likely to grant Daily Usage exemption requests for vehicles requiring 325 kWh of onboard energy storage capacity or less. In light of these restrictions, drive-cycle data and accurate, comprehensive physics math will be critical.

Infrastructure Delay: This exemption allows for delays related to permitting and construction processes — outside the control of your agency – for the installation of fueling/charging equipment. This type of exception is reserved for cases where the vehicle being replaced is 13 years old or older, and the exception is granted for up to two years, depending on the unique conditions of your project, and at the discretion of CARB.

ZEV Purchase: Like the Infrastructure Delay exemption, the ZEV Purchase exemption is limited to vehicles that are 13 years old or older. Exemptions of this type will be based on a list of vehicle types to be maintained by CARB (the “ZEV Purchase Exemption List”). CARB says they will publish the list no later than January of 2025. If your drive-cycle data and careful math reveals a case where you can’t find a feasible ZEV replacement, and you don’t find it on the ZEV Purchase Exemptions list, you can submit a ZEV Purchase Exemption Application. Such applications must be accompanied by photos, a list of frame attachments and documentation from at least two manufacturers that states the manufacturer doesn’t offer a suitable replacement.

    • If, despite your search, CARB is able to identify a manufacturer or dealer that offers a ZEV or NZEV in the next higher weight class that can perform the same primary intended function, CARB will provide you with the manufacturer or dealer name and CARB will deny the exemption application.
    • In the final ACF order, CARB says the ZEV Purchase Exemption List will include the following truck types: bucket, boom, dump, flatbed, stake bed, front-loader refuse compactor, side-loader refuse compactor, rear-loader refuse compactor, refuse roll-off, service body, street sweeper, tank/water, tow, car carrier, concrete mixer, concrete pump, crane, drill rig, and vacuum/”vac”.

Mutual Aid Assistance: This exemption is for vehicles associated with a mutual aid agreement[2] that’s already in place between your agency and other jurisdictions for vehicles used during officially-declared emergencies. CARB also wants to see documentation from three mobile ZEV fueling providers that show your vehicles cannot be refueled from 10 to 80 percent within 1 hour while in the field.

Backup: This exemption is for vehicles operated less than 1000 miles per year while not dedicated to officially declared emergencies.

Intermittent Snow Removal: This exemption is for vehicles equipped with a snow plow or snow blower mounting attachment and a control system for the plow or blower.

Non-repairable: This exemption is for vehicles that require replacement unexpectedly, due to an accident or other onetime event that renders the vehicle inoperative. In such cases, CARB is prepared to allow for replacement with a conventional vehicle of the same configuration and same model year or newer.

The Daily Use Exemption is likely to be the most challenging. It requires determining energy consumption requirements based on your drive-cycles. To accomplish this, CARB allows for two assessment methods.

  1. Calculate the vehicle energy storage requirements using fixed mile-per-kilowatt-hour (MPkWh) assumptions for each Class, from 2b to 8. The important thing to note here is that fixed MPkWh assumptions will not be sufficiently accurate for determining requirements:
    • in particularly hot (100+ deg. F) or cold (30- deg. F) climates,
    • for drive cycles with relatively high average speeds[3], or
    • for drive cycles with relatively steep grades over one leg of the drive cycle.
Note that temperatures above 110°F and below 25°F are associated with range-reduction of up to 30%.

The energy required to overcome aero drag increases with the cube of speed (MPH3); at highway speeds, aero drag accounts for more than half of all vehicle energy consumption.

As per the laws of physics (mass x gravity x distance) an 11,000 lb. Ford F-350 will consume a bit over eight (8) kWh just from the elevation change over a 2,000-foot change in elevation, and without the benefit of regenerative braking on a one-way trip, the ~70% you might otherwise recover is lost.

  1. As alternative to using fixed MPkWh assumptions, CARB allows for submitting measured[4] energy use from vehicles (and integrated power offtake equipment) already operated, and your measurement data must include loading and weight, drive-cycle grade, average ambient daily temperature and daily drive-cycle distance for at least 30 consecutive workdays from within last 12 months. CARB requires that you identify the lowest mileage drive-cycle for each day and exclude the three highest readings. To be granted the exemption, the highest remaining mileage or energy use number must be greater than the required range determined from your physics math.  CARB also requires an explanation of why appropriately-configured BEVs that are available cannot be charged during the workday, at the depot or within one mile of your drive-cycle routes.

Need Help Developing Your Compliance Plan?

As independent advisors, TerraVerde can help you:

  • Assess your compliance requirements
  • Develop your fleet electrification roadmap
  • Identify incentive funding sources and revenue opportunities

TerraVerde Energy is an independent energy consulting firm proudly supporting California public agencies since 2009 and serves as ACWA’s Preferred Provider for fleet electrification planning services. As your agency looks to identify the path forward, TerraVerde can provide your agency with a clear, actionable assessment of your options, costs, challenges, and opportunities; enabling your team to take an intelligent, risk-mitigated approach to fleet electrification. We welcome the opportunity to meet with your team and discuss your fleet electrification planning needs. Write to Phil Villagomez, Sr. Vice President ( to get started today.



[2] Agreements that establish the terms under which assistance is provided between two or more jurisdictions, and can be with and between private sector entities, NGOs, and other whole community partners. These agreements facilitate access to potentially needed vehicles, both prior to and following incidents or planned events. – FEMA, National Incident Management System Guideline for Mutual Aid, 2017

[3] Power required to overcome aero drag varies with the cube (to the power of three) of speed

[4] Measured, using telemetry or other data collection system that tracks mileage and energy use

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