(a) General.—The Secretary of Transportation shall prescribe regulations and issue orders that may be necessary to require that—
(b) Preemption.—
Notwithstanding section 20106 of this title, subsection (a) of this section does not prohibit a State from continuing in force a law, regulation, or order in effect on July 8, 1976, related to lighted markers on the rear car of a freight train except to the extent it would cause the car to be in violation of this section.