Washington DC road map, 1966 edition from Shell Oil
The reason this map is particularly interesting is how back in the day, road maps often showed proposed routes for Interstate highways either under construction or planned.
By this time, the continuation of I-70 (now I-270) to Union Station, along the Metropolitan Branch railroad, must have been scuttled, since it isn't shown on the map.
If you look closely at the bottom of the first image, you can see how I-66 was proposed to continue as a kind of beltway around the inner core of the city, with a routing just below U Street NW, connecting to I-95 around Florida Avenue.
I-95 was supposed to come from College Park to the DC/Maryland border around Michigan Avenue/Queens Chapel Road, and from there
I-295 was supposed to be west of its current routing, and then was to be routed through Langston Golf Course, Trinidad, and the Ivy City Railyard up along the Metropolitan Branch Railroad line, and then through the Fort Circle Parks greenway back to Queens Chapel Road.
The way that transportation planning worked back then, the subway and the freeways were planned simultaneously, e.g., how the subway is in the middle of I-66 once it leaves Arlington County in Virginia. Similarly, the red line was supposed to be bracketed by I-70, and the green line section in northern Prince George's County was supposed to be bracketed by I-95.
If you look at how much of the city was supposed to be destroyed by freeways, imagine all those sections of the city functioning something like the areas around the Southeast-Southwest Freeway (until recently) or South Capitol Street.