TO CREATE THE ARKANSAS DIESEL ENGINE FREEDOM ACT OF 2025; AND TO PROHIBIT STATE ENFORCEMENT OF FEDERAL REGULATION OF CERTAIN TYPES OF DIESEL ENGINES.

SB 478, known as the Arkansas Diesel Engine Freedom Act of 2025, aims to prevent state enforcement of federal regulations concerning certain diesel engines. The bill declares federal mandates requiring the use of diesel exhaust fluid for engines operating solely within Arkansas as null and void. It prohibits state agencies, political subdivisions, and their employees from enforcing such federal regulations on these "exempt engines," which are defined as diesel engines used exclusively within the state and not requiring diesel exhaust fluid. The act also establishes penalties for state entities that violate these provisions, including civil fines and suspension of enforcement authority.