New64

A tunnel. A channel. Bridges. A new interstate for a new generation. This will replace the nasty viaduct along the riverfront and provide new means to connect and new connections through the center city.

The tunnel curves to the southwest off the existing 64 just before the existing tunnel, then continues for awhile before turning northwest to follow baxter avenue, until curving west to run through the center of broadway. 

Low intensity plants are trees (with vertical roots), medium density plants are bushes, high intensity plants are plantings.

Based of some very terrible estimates this would cost between 8 million (two times highway construction) and 1 billion (skyscraper cost per sqft) I think that given proper conditions (cost mitigation/minimization) the costs would be about 20 million.

Two options for exits, below bridge right turn exits (would require complex and confusing turning around system above and below broadway, but ramps would not need to have stoplights along them), at bridge level with entrances to the dogbone roundabouts which go over the bridges.

If someone more familiar wishes to do a more realistic quote the construction from bottom to top is: 3' sidewalk with integrated vertical only curb, 8' dark green or dark red colored asphalt lane with three 1.5" painted lane markings (two solid white, one yellow), 6" vertical only curb, topsoil 2' at 1' depth, 6" vertical only curb) 8' asphalt lane with 1.5" painted lane markings (yellow and white), 6" vertical only curb, 1'8" topsoil at 1' depth and subsoil at 1' depth, 8" concrete wall 8' high