Peter Benjamin, who took over as the chairman of WMATA’s board of directors in January 2010 before ceding that position earlier this year, announced this morning will be stepping down. Benjamin, who represents Montgomery County and Maryland on the board, announced this morning that Maryland Governor Martin O’Malley wants to pursue a “clean slate” and new leadership.

Benjamin joined the board in April 2007; he has a long history of working with WMATA, including stints as Metro’s Chief Financial Officer and Director of Planning, and oversaw the organization’s leadership transition from John Catoe to current GM/CEO Richard Sarles. Benjamin told reporters this morning that the transition on the board would occur “very rapidly.”

Benjamin’s departure is the latest for a period of massive turnover for the influential board; longtime members Jim Graham and Chris Zimmerman have also left the board in recent weeks. At least one other Metro board member said the announcement had left the board “speechless.