I've thought about this. My thought has been, bump the street level up one story to create a pedestrian / bicycle promenade and move building entrances to the second floor. Keep the existing street below intact, with parallel parking etc. Essentially build a boardwalk above a commercial street, so that traffic can flow below. (Though for ventilation purposes, it would be best if most cars at street level were electric.)
Raising the street grade one story has been done before, when flush toilets were introduced in the late 1800's. Notably in Seattle and Chicago but in pockets other low-lying cities as well.