The Board of Public Works has approved seeking a public-private partnership to build the Purple Line in Montgomery and Prince George's counties.
The board voted 3-0 on Wednesday to move ahead with the plan.
Board approval was needed to go forward under a law approved by the General Assembly this year that created a framework to pursue public-private partnerships for infrastructure projects.
The board, which includes Gov. Martin O'Malley, Treasurer Nancy Kopp and Comptroller Peter Franchot, also will need to approve the final plan, which state transportation officials say could come before the board in December 2014.
The Purple Line would cost about $2.15 billion. The state is seeking about $900 million in federal money. The 16-mile light rail line would have 21 stations between Bethesda and New Carrollton.