California's quest to build the nation's first high-speed rail took another unexpected twist Thursday when the the man charged with leading the project announced he will resign in two months.

Roelof van Ark, who was appointed to lead the California High-Speed Rail Authority in May 2010, announced his resignation at Thursday's meeting of the rail authority's board of directors. At the same meeting, board Chair Thomas Umberg announced he will step down from his position as chair but remain on the board.

Shortly after the board meeting, which took place in Los Angeles, Umberg released a statement praising van Ark's work with the rail authority.

"With admiration, I would like to thank Mr. van Ark for his service to California and the high-speed rail project," Umberg said in a statement. "The announcement of his resignation will resonate throughout the State. His energy, passion and dedication to this critically important project are a testament to his character and his professionalism. We are extremely lucky to have his continued counsel and advice as we move to implement high-speed rail in California. I remain grateful for his professionalism and friendship."

Van Ark's resignation comes at a time when the project is facing severe criticism from state lawmakers and nonpartisan analysts over its recently released business plan, which showed the price tag of the rail project swelling to $98.5 billion. The estimated cost has more than doubled since 2008, when California voters approved $9.95 billion for the project.

Last month, a peer-review group recommended that legislators not fund the project until the rail authority addresses a series of flaws in its business plan, including uncertainty over funding sources and possible failure to comply with Proposition 1A.

While Gov. Jerry Brown remains supportive of the high-speed rail project, many legislators have turned against it and several introduced a bill earlier this week to halt all funding for the project.

Van Ark was one of several rail officials who attended a meeting on the project in Palo Alto last November. At that meeting, he defended the rail's business plan, which proposes to start construction of the line in Central Valley and which acknowledges that the project would not receive any private investment until after the first segment of the line is built.

He also defended the rail authority's controversial decision to start construction in Central Valley.

"This is the way the experts in the rest of the world have implemented the high-speed-rail systems in other countries," van Ark said at the November meeting.

Before becoming the rail authority's first CEO, van Ark had served as president of Alstom Transportation, a subsidiary of the French company Alstrom SA, which built TGV, France's high-speed rail system. He had also previously spent 20 years at Siemens, including a stint as president and CEO of Siemens Transportation Systems.

According to the Sacramento Bee, Van Ark cited personal reasons for his resignation.

"I need to focus myself more on my family, and maybe some other interests," he told board members.

Dan Richard, who was recently appointed by Brown to the rail authority's board of directors, is expected to replace Umberg as board chair next month, the Bee reported.