WASHINGTON U.S. Surface Transportation Board member Charles "Chip" Nottingham said he will not seek reappointment when his term expires Dec. 31.

Under federal law, STB members may continue serving for up to 12 months after expiration of their term, or until a successor is nominated by the White House and confirmed by the Senate.

President Obama has not announced a nominee to succeed Nottingham, the lone Republican on the three-person STB.

The agency's rail regulatory functions include approving mergers, line sales, line leases, line abandonments and imposition of labor protective conditions.

The other two members of the STB are Chairman Dan Elliott and Vice Chairman Frank Mulvey, both Democrats. Elliott was appointed chairman to succeed Nottingham in that post following Obama's becoming president.