Maryland Gov. Martin O’Malley announced Tuesday that the controversial Purple Line would be built as light rail, instead of bus rapid transit, in front of a crowd of purple-clad supporters and officials.

The 16-mile line would have up to 21 stations, providing a key east-west connection to Metro, MARC and Amtrak lines by 2018. Nearly all of it would run above ground, instead of tunneling under part of Silver Spring as some had hoped. And it would have an optional stop at Dale Drive in Silver Spring, another controversial spot.