((a)) ** .—** The Secretary of Transportation shall prescribe regulations and issue orders that may be necessary to require that—

((1)) the rear car of each passenger and commuter train has at least one highly visible marker that is lighted during darkness and when weather conditions restrict clear visibility; and

((2)) the rear car of each freight train has highly visible markers during darkness and when weather conditions restrict clear visibility.

((b)) ** .—** Notwithstanding , subsection (a) of this section does not prohibit a State from continuing in force a law, regulation, or order in effect on , 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.