AC Transit, the Bay Area's third-largest transit operator, has moved its assistant general manager into the position of interim general manager, replacing general manager Rick Fernandez, who is leaving after 13 years.

Mary King, a former member of the Alameda County Board of Supervisors, will serve as interim general manager while the district's board of directors searches for a permanent replacement, AC Transit said this afternoon.

"I pledge to the entire Board that I will do my best to continue the implementation of your policy," King said in a statement. King said AC Transit has "a duty to provide a safe and humane work environment for employees, and to serve the taxpayers and customers of AC Transit who rely on safe and dependable transportation."

Fernandez said Oct. 16 that he would leave AC Transit, which carries 260,000 weekday bus riders in a 360-square-mile area from Richmond to Fremont, as soon as an interim general manager could be found.

AC Transit and other public transportation agencies such as BART are enduring rough financial times. The bus system was forced to raise fares in July and is contemplating other money-saving moves.