After (practically immediately after) crossing the Potomac River via the Francis Scott Key Bridge, US 29 leaves the DC approach for the elevated Whitehurst Freeway; US 211 (pre-retraction) did not. Instead, it turned right along M Street, NW (a major thoroughfare, even then) to Wisconsin Avenue (originally the southern reaches of US 240) and then, turning right on Wisconsin, went down to the foot of Georgetown (Wisconsin @ K) where Wisconsin Avenue (and US 240) ended. However, US 211 still did not end (though it was actually *under* the WhiteHurst Freeway, and US 29, the two would only briefly interact once more). Coming east along K Street, underneath the Whitehurst Freeway (and US 29). K Street kept east to the confluence of K Street, the Potomac Freeway, and the eastern end of the Whitehurst Freeway (meeting both US 29 and Interstate 66 along the way). US 29 would pick up K Street here (which it does today), while Interstate 66 and US 211 would form a brief duplex (brief being only the length of the nearby Kennedy Center for the Performing Arts, which the Potomac Freeway passes to the east), where I-66 collects US 50 and starts the westward trek toward the Theodore Roosevelt Bridge, while US 211 continues east to meet US 1 at 14th Street and Independence Avenue (coming to that intersection, and its end, from the west, via Independence Avenue and Hains Point Park in the vicinity of the Washington Monument and the Lincoln and Jefferson Memorials).
Steve Kozel's "Roads To the Future" illustrates all those never-built urban freeways in the vicinity of the Kennedy Center and Key Bridge; all of them have a US route tie in somewhere (or would have, in the case of US 240 and I-66). US 240's southern augmentation (remember, US 240 was originally Wisconsin Avenue/Rockville Pike, especially in Montgomery County and the District itself) was the southern routing of I-70S (which, naturally, was never built). Because I-66 and US 29 (especially in Virginia) twist and turn about each other through most of the Interstate's length, there was an understandable thought that this would have contunued in the Federal city. However, signage that is still posted belies that theory; in particular, the in-city routings of US 29 and the old pre-decommissioning routing of US 211 and US 240. At the eastern approach to the Whitehurst Freeway (from K Street), you still have the option of remaining on K to Wisconsin Avenue (this is the Georgetown Park section of the city, still renowned as a shopping district; many trendy shops can be found here, including Dean and Deluca). A green button-copy sign used to be here indicating that K Street at this point was US 211 (US 29 was still the Whitehurst Freeway west, though US 29 was marked "south") and indicating that continuing west on K would take you to US 240/Wisconsin Avenue. (The Freeway did then, and does now, take a viaduct over both K Street and the C&O Canal.) The very fact that US 29 used the Key Bridge as its crossing into the District, while I-66 instead teamed up with US 50 to cross via the Teddy Roosevelt Bridge, and the Interstate's routing over the Potomac (but not the Whitehurst) Freeway, further proves that the US route being augmented was not US 29, but US 211 (which had not been truncated yet).