California's high-speed rail project is facing an audit from the U.S. Department of Transportation as costs continue to climb.

The inspector general's audit, announced Thursday, will examine the Federal Railroad Administration's oversight of nearly $3.5 billion in federal grant money awarded to the project.

It comes as the plan to bring travelers between Los Angeles and San Francisco in less than three hours faces growing scrutiny.

A business plan released in March shows the state does not have the roughly $30 billion needed to complete the first phase of the project between the Central Valley and San Francisco. The entire project, meanwhile, is expected to cost $77 billion. State auditors are also conducting a review.

The authority's new chief executive, Brian Kelly, has pledged more transparency about the project's troubles.