I don't understand what the federal clean air program has to do with anything? California can make whatever rules about their carpool lanes they want.

Just a guess, but the federal government probably paid for the roads, not the state. With that funding, are strings

The Clean Air Vehicle (CAV) program requires federal approval under Section 166 of Title 23 of the U.S. Code.

The federal government is notnot be extending the program, which means the underlying authority for the program expires.

California passed legislation to extend the program, but this extension is contingent on federal approval, which was not granted.