Do California's Emissions Standards Affect Fleets in Other States?

In response to recent federal actions rescinding California's emissions waivers, this report explores how California's vehicle emissions standards continue to shape national fleet behavior through adoption by 17 states and Washington, DC. It outlines the legal and regulatory framework that enables California's influence, including the Clean Air Act's waiver system and the role of the California Air Resources Board (CARB). The report highlights the effectiveness of California's Advanced Clean Cars and Trucks programs in accelerating zero-emission vehicle (ZEV) adoption, with Colorado serving as a key example of successful policy replication. Legal challenges, such as Diamond Alternative Energy v. EPA, underscore the growing tension over state-level authority and the future of emissions regulation. Guidehouse Research recommends that regulators act strategically to preserve waiver authority, that states coordinate legal defenses, and that OEMs align product planning with CARB-aligned markets to mitigate risk and maintain competitiveness.