Les Klein has an idea for Toronto's much-reviled Gardiner Expressway that runs along the lakefront – instead of hating it like nearly everyone else, let's wrap it in a giant Green Ribbon.

"I happen to always have loved the Gardiner," says Mr. Klein, principal and co-founder of Toronto-based Quadrangle Architects Ltd. "I came into town when I was 25 for my first job and I remember coming over the hump [a startling bump in the expressway, since smoothed over, near the Humber River]. I thought, this is a beautiful way to enter the city."

Right now, most planners and politicians think the Gardiner is anything but beautiful. They are ruminating over what to do with the crumbling, congested expressway, with the choices seeming to be either to rip it down or patch it.

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Mr. Klein has a different idea. He has drawn up a proposal to build what he calls the Green Ribbon – a seven-kilometre, landscaped roof over the elevated highway.

The Green Ribbon would keep the Gardiner functioning and intact, minimize future repairs by protecting it from bad weather and also create 32 hectares of recreational parkland above the road, he says.

The millions of dollars now being contemplated to repair the Gardiner or tear it down could, after existing repairs are made, be better spent by protecting it with a park over the top, he contends.

The Gardiner now handles 200,000 cars and trucks a day (though it was originally built for 70,000 vehicles), and the bill to keep it from falling down is now estimated by Toronto's city engineering staff at $505-million over 10 years. This summer alone, critical repairs just to keep part of the elevated road safe are costing taxpayers $9-million .

Tearing the highway down would be costly and disruptive, too, Mr. Klein says. "I don't believe tearing it down would be viable. Our approach to transportation may change, but for now it's a key component of moving people and goods in this region."

A third alternative, "burying" the Gardiner by replacing it with a new underground expressway, would run into the billions and pose engineering and construction problems, because much of the land where the Gardiner now sits is composed of landfill that was deposited in the 19th and 20th centuries, so the water table is perilously close.

All this makes the Green Ribbon not only visionary, but practical, Mr. Klein contends. It could be built for approximately $700-million and brings benefits that would enhance Toronto's infrastructure and competitiveness.

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Mr. Klein envisages virtually the entire length of the downtown expressway being covered by a series of bridge-like structures, landscaped with green space, foot and bicycle paths and sprinkled with cafes, boutiques and small galleries.

Pedestrians and cyclists would access this leafy upper deck via stairs, elevators and ramps at a series of "nodes" that would also serve as struts to hold up the Green Ribbon.

As an engineering feat, it's not as hard as you might think, Mr. Klein says. At its lowest point, the Gardiner is about 8.5 metres above the ground – the Green Ribbon would add roughly another 8 metres beyond this.

All of the structure would be built independently from the roadway below. "You don't want to add any more load to that [road] structure."

A beribboned Gardiner would be easier to maintain because it wouldn't need to be salted in the winter, and it would be safer too, because the east-west route often confounds drivers who get the glaring sun in their eyes, he says.

A series of solar panels at points along the Green Ribbon could provide power for lighting the covered roadway, too.

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Putting a park in the air is not unprecedented – in New York City, a not-for-profit group worked since 1999 with that city to open the High Line, a 2.3-kilometre linear park along an abandoned railway spur. The High Line, which opened in 2009, attracted more than two million visitors in its first year alone. The park continues to expand, with a third section due to open next year, and it has spurred full-scale gentrification and redevelopment of New York's once-sketchy Meatpacking District.

Mr. Klein concedes that funding a $700-million project like the Green Ribbon would be a challenge for cash-strapped Toronto. And other experts, while intrigued by the idea, are not 100 per cent sure it's a panacea.

"If Toronto is serious about being a sustainable and green city in the 21st century, it must focus on improving public transport and intra-regional light rail services. The Green Ribbon will do little to achieve this goal," says Robert Maguire, project director at Wood Wharf, a major redevelopment next to London's Canary Wharf.

"But it will send an important signal that Toronto's priorities are shifting increasingly away from the car toward the pedestrian," adds Mr. Maguire, a former Toronto city planner.

The city is already being compelled by senior governments to consider new revenue tools to pay for improving its creaky transportation infrastructure. And Mr. Klein has already been discussing financing models with several Bay Street firms.

Some of the financial models are complicated, and some, such as issuing private debentures, would require changes in provincial legislation for municipal infrastructure funding. But they're not impossible.

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He also sees a big idea like the Green Ribbon as consistent with the vision of Toronto's leaders in the 1940s and '50s, who planned the Gardiner itself as a bold game changer that would make the city more competitive: "When it was built, these kinds of ideas were the essence of progress."

"It's also the most green thing you can do," says Mr. Klein, whose firm is known for "adaptive reuse" projects such as the MuchMusic building (formerly CityTV) on Queen Street West. "If you tear it down and take away all the pieces, you lose all that embedded energy."

Something has to be done soon, no matter what, he points out. In 2012, there were six reported instances of falling chunks from the highway, whose oldest sections will turn 58 in August, and city engineering reports express concern about more of what they ominously call more "punch-throughs."

"One of the biggest challenges facing Western society at moment is that, by and large, for the last 40 years, we have postponed spending on infrastructure under the guise of fiscal responsibility," Mr. Klein says.

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Editor's note: This article has been corrected to reflect the cost estimate of repairing the Gardiner as $505-million, rather than billion.