; or (3) security personnel, dispatchers, locomotive engineers, conductors, trainmen, other onboard employees, maintenance and maintenance support personnel, bridge tenders, and any other employees of railroad carriers that the Administrator determines should receive security training under this section or that is receiving security training under other law. 17. Voluntary use of credentialing (a) In general An individual who is subject to credentialing or a background investigation may satisfy that requirement by obtaining a valid transportation security card issued under section 70105 of title 46, United States Code. (b) Issuance of cards The Secretary of Homeland Security— (1) shall expand the transportation security card program, consistent with section 70105 of title 46, United States Code, to allow an individual who is subject to credentialing or a background investigation to apply for a transportation security card; and (2) may charge reasonable fees, in accordance with section 520(a) of the Department of Homeland Security Appropriations Act, 2004 ( 6 U.S.C. 469(a) ), for providing the necessary credentialing and background investigation. (c) Definition In this section, the term individual who is subject to credentialing or a background investigation means an individual who— (1) because of employment is regulated by the Transportation Security Administration, Department of Transportation, or Coast Guard and is required to have a background records check to obtain a hazardous materials endorsement on a commercial driver's license issued by a State under section 5103a of title 49, United States Code