The provisions of § 391.21 (relating to applications for employment), § 391.23 (relating to investigations and inquiries), and § 391.31 (relating to road tests) do not apply to a driver who was a single-employer driver (as defined in § 390.5 of this subchapter) of a private motor carrier of passengers (business) as of July 1, 1994, so long as the driver continues to be a single-employer driver of that motor carrier.