The F.G. Gardiner Expressway, an expressway built along the shore of Lake Ontario for the purpose of moving traffic into and out of Toronto's downtown core, a task at which if fails due to lack of capacity. it is also an effective barrier between the people of Toronto and the lake.
Maintained by the City of Toronto from Highway 427 in the west side of the city to 3 km west of the Don Valley Parkway at Lakeshore Boulevard East. The part west of the Don Valley was to be the start of the Scarborough Expressway, which was cancelled in 1971.
It's now old and scary, driving beneath it on Lakeshore Boulevard you can see the spalling concrete and the exposed rebar.
There are continual studies afoot to discuss tearing it down, perhaps to replace it with a below grade (i.e., buried) roadway. The useless extension from Yonge street to Leslie is being torn down in 2000-2001. It's a good start.