The pedestrian piazzas being carved out from vehicular thruways at Times Square and Herald Square in New York City are testimony to the critical need for public space in our cluttered mega-cities. But public space is not merely the passive residue of a decision to ban cars or a tacit invitation to the public to step into the street. It must be actively created and self-consciously sustained against the grain of an architecture built as much for machines as people, more for commercial than common use.

In a word, public spaces are built, not natural; they are the result of constructive intervention rather than laissez-faire disinterest. There is an “art of public space,” which requires more than no-car signs, traffic cones, concrete barriers, tables and chairs. Happily, New York possesses an urban resource ideally suited to creating public space: artists. Now that the Department of Transportation has temporarily liberated some space from automobiles–city officials will decide at the end of the year whether to extend the traffic ban–it needs to shape that space in ways that invoke democracy, attract usage and make it “public” in the deep sense of commonality, interactivity, connectivity and community. The idea of creative public space will not fail, but New York may fail to realize it.

To succeed, public space will demand greater public investment and better understanding of the role artists and the arts play in putting such investment to imaginative uses.

These notions yield two mandates. First, they call for greater public investment in public space and in the arts that help shape such spaces. And second, they call for greater understanding of the role artists and the arts play in putting public investment to imaginative uses.

The role of artists here is not just to install a sculpture, plant a garden or make a mural (although these would be nice). Rather, it is to envision a space where visitors are encouraged (but not constrained) to move in certain ways, inspired (but not forced) to use the space creatively, pulled (but not pushed) to feel they are helping to shape the space even as they enjoy themselves in it. The ancient agora, or civic marketplace, of democratic Athens and the covered arcades of nineteenth-century European towns exemplify a spirit where public things (literally res publica, the origin of our word “republic”) become paramount. Entertainment and commerce are necessary and important, but they “work” because people are drawn into public spaces for other reasons: to play in the company of others, to watch one another and see others with fresh vision (here the fabulous red stairs atop the TKTS booth at Forty-seventh Street make a splendid start), to interact with strangers, to get out of private space and into common space.

Think of Las Ramblas in Barcelona, the carnivalesque pedestrian esplanade that is the heart of the city’s cultural and commercial district, teeming with street artists and mimes as well as pickpockets and tourists, equally welcoming to the opera house and the old market (La Boqueria). Or visit the Hackesche Höfe in Berlin, where linked buildings rise around a warren of courtyards that permit small crafts factories, theaters, art galleries, restaurants and residences to coexist in an atmosphere of energetic conviviality that is both a reminder of the nineteenth century and a harbinger of the twenty-first.

Closer to home, consider Millennium Park in Chicago. The city got it right by engaging artists, designers and architects to collaborate in creating the space, with Frank Gehry’s Pritzker Pavilion, Jaume Plensa’s interactive Crown Fountain and Anish Kapoor’s Cloud Gate sculpture. Together, these interactive attractions have made the Millennium Chicago’s most popular recreational and leisure destination.

Yet artistically inflected public spaces in our cities need not encompass only upscale parks and tourist destinations. In 2008 the extraordinary artist and director Robert Wilson brought a team of artists and sociologists (I was among them) to Gunpowder Park just outside London and, working with a local visionary consultancy and neighborhood residents, helped transform what had been a World War II munitions testing ground into an interactive commons. It is now widely used by the multicultural community that helped create and define it.

What might a creative blending of artistic and popular imagination come up with in Times Square? Imagine an open mini-bandstand or stage accessible to dance or theater or music groups for free performances; an erasable mural and graffiti wall for children to deface, reface and efface; a life-size chess set; molded benches where people can idle and gawk at others doing the same thing; artist installations around themes such as “recycling,” “imagination” and “childhood”; mirrors (ordinary or funhouse) to watch yourself watching others; a hollowed-out, anchored taxicab or subway car in which kids can play and others can rest; a rotating display of banners and flags designed by schoolchildren, art students and professional artists. Then add shuttle buses to other arts destinations in the city, like the Lower Manhattan arts district, where galleries and theaters like 3-Legged Dog have sprung from the ashes of 9/11; the Brooklyn Academy of Music; the Fifth Avenue museum district; or Harlem.

Here, then, is the challenge: the cars and trucks that clogged up Times Square have been sidetracked, if not quite removed. What will fill the empty streets and turn the famous piazza into a true commons, a place whose “public” brand reflects the reality of artistic imagination and the public’s ongoing participation in the civic republic? Getting rid of the traffic was the easy part. Now comes the real work: to secure adequate funding, to enlist artists, to fill in the newly created residual void.