Critical to a tamed street environment conducive to this air rights development, are center loader access ramps for the freeway- IOW the ramps to or from the freeway have short tunnels to thus not load by the left hand curb but rather from the middle of a frontage-service road.
This center loader design preserves the curbside for lower speed uses, and can be seen in renderings of the proposed Washington, D.C. I-395 redevelopment project just south of Massachusetts Avenue in Washington, D.C.
This design should be a mandatory retrofit for existing urban freeways- at least those built below ground level, as it has been the ramp interface rather than the existence of the mainline freeway itself, that causes the ripple of intimidation for pedestrians and to a degree local vehicular traffic depending upon the design and location of cross-streets.
An example of such as a retro-fit can be found in the recent proposals to construct 'air rights' development atop I-395 (re I-95) in Washington, D.C.
As far as I know, the issue of center rather than side loader freeway access ramps remains unaddressed by transportation planning advocacy organizations, owing to a dogmatic doctrinaire stance against the very concept of urban freeways preventing them from finding let alone appreciating such critically needed design improvements.