Probably some on this forum have seen the area around Sears Tower where the city streets are all overpasses above ground level, with the buildings' underground service levels actually built in the open air at ground level. The development of Illinois Center, Lakeshore East and Millennium Park over former railyards saw this taken to another level (with two layers of service streets under the city sidewalk). Discussions of I-345 have generally presented either a costly Big Dig, a modification and updating of the status quo, or its replacement with a boulevard and the crosstown traffic can take Loop 12 or 635 or stay home. Sadly none of these is particularly adequate for a city like Dallas.
The only option that gets us closer to where we want to be while allowing us to be where we are in the meantime would be a fourth option. Let's start improving that option: Tear down 345. Rebuild the lanes immediately, with rapid crane installation of large pre-prefabricated concrete units from one or more adjacent staging yards. But rebuild it now within chest height of ground level, using its current alignment as an end-to-end through route without more than a couple of local on- and off-ramps if any. Simultaneously, build sufficient columns between the north- and south-bound halves that the treelined urban boulevard level will be 20' above the mainlanes of new-345. Its substructure is built now, to be finished on top without need for any later closures of I-345. In phases, as concurrently as practicable, Canton, Main, and the rest of the streets between Deep Ellum and downtown would need to be built up to new ground-level intersections with CTroyMathis Blvd. It can get lined with apartments, civic buildings and workplaces on both sides whose loading docks require no sidewalk cuts, being 20' below the street at ground level.