It doesn’t happen often, but once in a while an utterly captivating idea for urban reinvention comes along. Toronto architect Les Klein’s proposal for a green roof over a seven-kilometre stretch of the Gardiner Expressway is one such idea.

Klein, a founding principal at Quadrangle Architects, envisions a linear park built eight metres above the Gardiner and lined with trees, pedestrian walkways, bike paths and concession stands. The proposal would transform the existing highway between Dufferin and the Don Valley Parkway from an eyesore into an innovative public space.

New York’s recently opened High Line Park hints at what Toronto’s Green Ribbon could be like, which is to say, delightful. The High Line has been swamped with visitors since the first section opened in June.

The original rail line, built in the 1930s, shut down in 1980. The structure has been re-invented as a park with meandering walkways and greenery.

But it is the park’s elevation that makes it unique. Instead of gazing up at the city from street level, visitors look down on a sea of rooftops, some of them transformed into colour-saturated flower gardens.

Klein’s green roof would be less disruptive to traffic than tearing down the Gardiner, and even at $500 million to $600 million, it would be significantly cheaper than burying the road. A rooftop park would protect the highway below from the elements. It would be embraced by runners, walkers, and cyclists in summer and by cross-country skiers in winter.

New York is not alone in building an elevated linear park. The Promenade Plantee in Paris is an elevated park on a converted rail viaduct. St. Louis, Philadelphia, Jersey City, Chicago and Rotterdam are all contemplating similar projects. The Green Ribbon would be a unique, made-in-Toronto variation on this theme.

It would also be an innovative solution to the problem that is the Gardiner. For all these reasons, Klein’s idea is worthy of serious consideration.