Montgomery County began studying transit options for the corridor as early as 1986 and continued to study, litigate and debate it, until work began in 2017. A trolley between Bethesda and Silver Spring went through several iterations including the Georgetown Branch Light Rail Transit, the Inner Purple Line, the Bi-County Transitway and finally the Purple Line - a light rail train from Bethesda to New Carrollton, MD. Each iteration included plans to pave a parallel extension of the trail between Bethesda and Silver Spring and using the existing Air Rights Tunnel. However, in 2011 MTA announced that the cost of building the extended trail would be $103 million, much more than the previously estimated $65 million. Half of the cost would result from widening the Air Rights Tunnel to include the trail with the train. Instead, the county made plans for a 2nd trail tunnel, parallel to the transit tunnel, built, in part, under a new Air Rights building.