The National Capital Region Transportation Planning Board voted unanimously today to add the Purple Line to its long-range transportation plan, a key approval in the lengthy process to build the new line. Whether the proposed 16-mile line connecting Bethesda to New Carrollton will be light rail or bus rapid transit is still an open question, but a decision on that could happen as early as the end of the summer, assuming the next step, an environmental review process, doesn’t drag on and on.