Darling was named acting administrator in August when Administrator Anne Ferro left after running the agency for five years.
President Obama has yet to nominate a successor to Ferro, however, and acting administrators are only allowed under the law to have that title for a period of time. Darling’s tenure expires March 23.
Foxx has “delegated” Darling, who is FMCSA’s chief counsel, to perform the duties of administrator.
“Thus, consistent with the Vacancies Act, he will continue to perform the duties of the administrator but will no longer be referred to as the acting administrator,” the Department of Transportation said in a March 23 statement.