(1) Except as provided in paragraph (2) of this subsection, this subchapter and section
31102 of this title do not
(A) prevent a State or voluntary group of States from imposing more stringent standards for use in their own periodic roadside inspection programs of commercial motor vehicles;
(B) prevent a State from enforcing a program for inspection of commercial motor vehicles that the Secretary decides is as effective as the Government standards prescribed under subsection (b) of this section;
(C) prevent a State from participating in the activities of a voluntary group of States enforcing a program for inspection of commercial motor vehicles; or
(D) require a State that is enforcing a program described in clause (B) or (C) of this paragraph to enforce a Government standard prescribed under subsection (b) of this section or to adopt a provision on inspection of commercial motor vehicles in addition to that program to comply with the Government standards.
(2) The Government standards prescribed under subsection (b) of this section shall preempt a program of a State described in paragraph (1)(C) of this subsection as the program applies to the inspection of commercial motor vehicles in that State. The State may not enforce the program if the Secretary
(A) decides, after notice and an opportunity for a hearing, that the State is not enforcing the program in a way that achieves the objectives of this section; and
(B) after making a decision under clause (A) of this paragraph, provides the State with a 6-month period to improve the enforcement of the program to achieve the objectives of this section.