49 C.F.R. § 601.4
The Administrator is responsible for the planning, direction and control of the activities of FTA and has authority to approve Federal transit grants, loans, and contracts. The Deputy Administrator is the "first assistant" for purposes of the Federal Vacancies Reform Act of 1998 (Pub. L. 105-277) and shall, in the event of the absence or disability of the Administrator, serve as the Acting Administrator, subject to the limitations in that Act. In the event of the absence or disability of both the Administrator and the Deputy Administrator, officials designated by the agency's internal order on succession shall serve as Acting Deputy Administrator and shall perform the duties of the Administrator, except for any non-delegable statutory and/or regulatory duties.
49 C.F.R. §601.4