Years ago, during the 1960s, the idea of a vehicular tunnel beneath K Street was advocated as the best way for achieving the crosstown D.C. link for I-66. It was promoted by opponents to the previous plan from the 1955 Inner Loop study for a new right of way swath freeway along the southern edge of Florida Avenues and U Street, requiring removing hundreds of buildings; the K Street tunnel meanwhile would have removed only a relative handful at its eastern connection, largely to clear the Carnegie Library at Franklin Square.
As such, the I-66 K Street Tunnel and had the support of US NCPC's Elizabeth Rowe, who was also connected with the private organization, the Committee of 100 on the Federal City that had been founded by Delano during the 1920s..
Planning for the WMATA rail subway system had accommodated that with space above the southern end of the Farragut North subway station platform. The need for this connection was initially created by a decision to provide two separate stations for Farragut North and West, rather than a consolidated facility accommodating both station-stops, to avoid excavating beneath the Farragut Square park just south of K Street that would have required removing a number of trees.
During the mid 1970s, the I-66 K Street Tunnel would be 'de-mapped' to scavenge its funds for speeding construction of the WMATA rail subway system, with such reasoning that the world was going to run out of petro by the 1990s hence somehow rendering private automobiles obsolete, and that Virginia was not going to build their connecting inside the Beltway segment of I-66- both which proved to be false.
Subsequent planning following the 1970s 'de-mapping' of the I-66 K Street Tunnel now fails to respect its underground right of way space, and thus needs modification for such.
A recent article in Greater Greater Washington details the two main design options now/recently under formal consideration, with an estimated total monetary construction cost of $130 million. See official report.
Option One places a staircase from the proposed connector tunnel to the platform below in the way.
Option Two places a new connecting section from the proposed connector tunnel to the existing mezzanine platform.
As it is the area of the southern platform of the Farragut North station that would be connected to the new pedestrian tunnel at the area beneath K Street, this existing area would need an extension to just south of K Street in order to provide the space for this connect that would avoid the space beneath K Street and hence accommodate both this new underground pedestrian connection and the K Street tunnel. This would have to be a variant of Option One, as a continuous mezzanine level platform conflicts with the space for the K Street tunnel.
A google map photo shows three trees along the Farragut Square park's northern edge, which extends northward past the customary southern edge of the K Street right of way.