Tactical urbanism is the key.
Tactical urbanism, coined from the book with the same name, is what Portland has been doing for ages during the Intersection Repair projects. It is a low-cost and learn-by-doing strategy reminiscent of so many social action strategies of the 60s except this time the result is physical changes within neighborhoods that avoid long planning processes.
San Francisco is the latest to try tactical urbanism by welcoming artists, urban designers and others to set up their innovations along Market Street. A few selections occupying the upper register of my cool-o-meter: Data Lanterns that glow brighter to announce arriving trains, metal walls that turn into a musical instrument on touch, and street seats made from compacted mushrooms for composting afterwards.