Thousands of music fans are packing Hart Plaza this weekend for the annual jazz festival, but for much of the year, Hart Plaza remains largely empty.

Now the City of Detroit is beginning to mull how to enliven Hart Plaza, including whether to scrap the current design that hails from the 1970s and start over with something entirely new.

Mayor Mike Duggan's administration told me it's way too early to talk about a new future for Hart Plaza. There are no solid plans yet and probably no money to accomplish any if there were.

But it's well understood among professionals who follow the revitalization of Detroit's waterfront that the city's planners are looking at a big change there. For despite the crowds that fill the plaza for special events like the jazz fest, a redo of Hart Plaza is badly needed and long overdue.

The city created Hart Plaza in the mid-1970s from a design by Smith, Hinchman & Grylls at a time when monumental open spaces on a European model were viewed as essential to a city's viability.

Famous models like Piazza San Marco in Venice and Piazza del Campo in Siena provided inspiration for mid-century planners — vast paved spaces that created crossroads of humanity and that filled with thousands of citizens during celebrations, protests, and special events.

Indeed, the fall of communism in the late 1980s was largely accomplished in the great civic plazas in Eastern European capitals that gave millions of people a place to voice their protests — venues for the peaceful revolution to actually happen.

But current thinking about what makes a good urban gathering spot has changed a lot since the 1970s. Today we understand that vast expanses of concrete and asphalt do little or nothing by themselves, especially when, as in the declining Detroit of the '70s, the city adopted a bunker mentality toward its riverfront, building the Renaissance Center as a fortress with little or no interaction with the plaza right outside.

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Today, instead of Hart Plaza's passive vast emptiness, planners including those working in Detroit try to provide much more active programming in the form of music, food trucks, basketball hoops, volleyball nets and much more.

Campus Martius Park is a good example. Created in the early 2000s, Campus Martius Park is heavily programmed with activities, including music in the summer and ice skating in the winter, with an array of food and drink options year-round.

Planners like New York-based Project for Public Spaces have worked with the city and private entities like Dan Gilbert's Bedrock real estate arm to scatter street furniture, artwork, games, rental bikes, and more in and around Campus Martius.

Just in the past year or so, Detroit has added the Esplanade — a landscaped walkway down the center of Woodward running south from Campus Martius — and Spirit Plaza, the area in front of the Coleman A. Young Municipal Center that was recently closed at Woodward to vehicle traffic.

Connecting downtown and the riverfront

Enlivening Hart Plaza would complete that stretch and better connect the rest of downtown to the riverfront.

"This is the potential and important crown jewel as you start thinking about access to the riverfront and the terminus of Woodward," said Michael Johnson, co-director of the urban design practice at Detroit-based SmithGroup, a leading architecture and design firm. "It’s an incredibly interesting prospect that has to be done right."

But redoing Hart Plaza won't be a simple matter of planting a few more trees and some grass. For one thing, the plaza sits atop a catacomb of below-ground spaces, including restrooms and food preparation areas.

Then, too, the plaza is dotted with several major works of public art that must be treated respectfully, from the Dodge Fountain designed by Isamu Noguchi and Walter Budd in the late 1970s to memorials honoring the Underground Railroad and Michigan's labor legacy.

Jefferson, Atwater pose problems

Perhaps most significantly, any redo of Hart Plaza must grapple with even larger planning questions. Among those:

What's the role of Jefferson Avenue downtown? Today it functions as a sort of extension of the Lodge Freeway, funneling traffic on and off the expressway in the heart of downtown. But the wide, traffic-choked Jefferson cuts off Hart Plaza from the central business district (CBD) — a problem for any attempt to bring more people and activity toward the riverfront.

Should Jefferson go underground through that stretch, allowing a continuation of Spirit Plaza to directly connect with Hart Plaza? That's just one possibility.

"What role does Jefferson play in the future of the city?" Johnson said. "Can you adapt that in any way to better connect the CBD to our riverfront? Those are big planning level conversations that have to take place."

A related question is what should happen with Atwater Street, which currently goes below grade under Hart Plaza.

And what should happen with the roughly 20-foot grade change from Jefferson down to the waterfront? When the French entrepreneur Cadillac founded the settlement in 1701, there were bluffs lining the waterfront, bluffs that have been mostly bulldozed and smoothed out.

Hart Plaza deals with the grade change with stairs in places and gradually sloping the plaza toward the river. But planners could decide to change that in some way.

Breaking down barriers

Nobody in the mayor's office is talking publicly about it yet, but the buzz I'm hearing is that nothing is off the table.

In an important way, the problem with Hart Plaza is not just the emptiness of all that concrete but the lack of activities immediately surrounding it. Jefferson remains a barrier, while the Renaissance Center, even after its terrific redo in recent years that saw the creation of the Wintergarden and waterfront plaza, still remains something of a fortress on the river.

The great European plazas that inspired places like Hart Plaza, the civic squares in Venice and Siena and other cities, tend to be surrounded by engaging buildings that make the plaza themselves natural gathering spots. That's what's missing here.

"Hart Plaza is less of a design issue and more of a demand issue — we need a reason to go there," said Robin Boyle, former chair of urban planning at Wayne State University.

Dan Kinkead, co-director of urban planning at SmithGroup, agreed.

"We put so much pressure on the space itself to perform that we forget that it’s a dance," he said. "It’s a kind of dual exchange between that space and the things that surround it.”

So deciding the future of Hart Plaza will force the city to ask a lot of related questions: The future of the nearby Joe Louis Arena site, or what areas of the RiverWalk should be busy and programmed and which should be left more passive for people to just sit and enjoy the views.

All of those questions are on the table.

It may help to remember that it takes a long time to create a great city. Planners have been offering ideas for Detroit's central riverfront for a century or more, even since it began to shrug off its industrial past. Hart Plaza emerged in the 1970s only after decades of debate and delays.

The city made plenty of mistakes along the way. But now it appears Detroit will try again.

That's good, and it's overdue. This time, perhaps, we'll get it right.

Contact John Gallagher: 313-222-5173 or gallagher@freepress.com. Follow him on Twitter @jgallagherfreep.