Midterm Review

When the California Air Resources Board (ARB) adopted the Advanced Clean Cars (ACC) program in 2012, the agency committed to conduct a comprehensive midterm review of three elements of the program - the zero-emission vehicle (ZEV) regulation, the 1 milligram per mile (mg/mi) particulate matter (PM) standard, and the light-duty vehicle greenhouse gas standards for 2022 and later model years. A midterm evaluation (MTE) of the light-duty vehicle greenhouse gas standards for 2022 through 2025 model years was also conducted at the national level and ARB staff collaborated with the U. S. Environmental Protection Agency (U.S. EPA) and the National Highway Traffic Safety Administration (NHTSA) to review the standards since the California program closely mirrors the national program for these model years.

ZEV Regulations
ZEVs are essential for meeting California's long term greenhouse gas and criteria air pollutant reduction goals. Staff's review will evaluate the growing ZEV market and consumer acceptance of those vehicles. Additionally, staff is analyzing consumer survey data of plug-in electric vehicles, infrastructure development, and a review of the technological advancements in ZEVs since the 2012 rulemaking. Accordingly, ARB has initiated a number of outside studies to evaluate consumer vehicle purchase decisions and how different types of ZEVs and plug-in hybrids are being used within a household.  Results of this analysis are presented in the staff’s midterm review report.

PM Standard
When the Board adopted the 1 mg/mi PM standard, they directed staff to verify the current gravimetric measurement method's ability to accurately measure PM emissions at likely compliance levels and re-examine the timing and stringency of the standard. The measurement method's ability was verified in October 2015 when the results of the multi-year evaluation were presented to the Board. Subsequently, a technical feasibility study of PM emissions control from projected low-greenhouse gas vehicle technology vehicles was conducted. The results from this, and other studies, are reflected in staff’s midterm review report and inform staff’s recommendations to the Board on the feasibility of the 1 mg/mi standard and whether it is appropriate to move the 2025 implementation date forward.

Greenhouse Gas Regulations
The Board directed staff to collaborate with U.S. EPA and NHTSA to review the federal light-duty greenhouse gas standards for 2022 through 2025 model years. This review included collaborating on a second joint Technical Assessment Report (TAR) to re-assess the technical assumptions and analysis used to develop the greenhouse gas standards. The Draft (Joint) TAR was published for public comment in July 2016. After reviewing public comments, U.S. EPA updated their analysis and published for public comment in November 2016 a Proposed Determination that the 2022 through 2025 federal standards remain as adopted.  Subsequent to a review of public comment, U.S. EPA concluded their midterm evaluation and published a Final Determination in January 2017 that affirmed the existing federal greenhouse gas standards would remain as adopted.

ARB's technical assessment was performed in parallel and is reflected in staff’s midterm review report. As directed by the Board, the midterm review report also presents staff’s analysis of consumer purchasing trends and changes in California's fleet mix to evaluate any effect of a potential shift in vehicle footprint size to higher polluting vehicles and the reclassification of cars as trucks that deviates from the fleet size and category mix originally projected in 2012.


California's Advanced Clean Cars Midterm Review Report new

This report and its appendices encompass ARB’s technical analysis for the midterm review of the adopted LEV III GHG and PM emission standards and ZEV requirements.  The report includes recommendations to the Board for next steps for each of the adopted requirements.


January 18, 2017 Press Release new

CARB Releases Major Report on the Future of Ultra-Clean and Zero-Emission Vehicles
In-depth California Midterm Review finds electric drive technology accelerating and ahead of schedule


Full Midterm Review Report with all Appendices:

Summary Report for the Technical Analysis of the Light Duty Vehicles Standards, with Appendices (PDF - 18.74 MB)


Midterm Review Report and Appendices as Separate Files:


Summary Report for the Technical Analysis of the Light Duty Vehicles Standards (PDF - 2.7 KB)



Information Updates to the Board

In March 2017 staff presented the Board with the results of ARB's midterm review. In addition, staff has already provided yearly status updates to the Board since the ACC regulations were first adopted in January, 2012. Links to these status updates are provided below.


March 23rd and 24th, 2017 board hearing


July 21, 2016 board hearing


October 22, 2015 board hearing


October 23, 2014 board hearing

  • Staff presentation

  • Focus: Updates on greenhouse gas technology technical assessment work with Federal agencies, ZEV-related research contracts related to consumers, and the feasibility of particulate matter measurement


October 24, 2013 board hearing

Advanced Clean Cars Symposium: The Road Ahead

The staff of the ARB brought together automakers, suppliers, and other clean car stakeholders on September 27-28, 2016 to look at technologies that expand upon the draft Technical Assessment Report:


Additional Information:


Active Studies:

This page last reviewed June 2, 2017