The Gardiner Expressway has become Toronto’s great quagmire. The elevated, concrete traffic artery has sliced through the downtown core since 1965, and has been the bane of urban planners, real-estate developers, environmentalists, and commuters ever since. The debate over how to update the decaying structure is a heated one. Should we tear it down? Repair it? Build under it? Around it? Through it? How about on top of it?