User talk:2600:1700:AB20:1C50:38EB:6F9E:57C3:9C6D

United States Emissions
"Under federal law, the state of California is allowed to promulgate more stringent vehicle emissions standards (subject to EPA approval), and other states may choose to follow either the national or California standards."

This statement is incorrect. The original author must be ignorant of US law. Under the Constitution powers not granted to the Federal government pass to the states or to the people respectively. The states may individually pass laws more stringent than Federal laws or in the absence of Federal laws. Such laws are subject only to the United States Supreme Court and may be struck down only if found to be Unconstitutional.

Under the Constitution of the United States, any state may promulgate more stringent vehicle emissions standards. This is not subject to EPA approval.