Of Toronto's transit network as a whole, I'd say it's the streetcars which are most iconic. Everywhere else in North America, streetcars are either refurbished heritage runs or sophisticated light rail using shiny new equipment. Toronto's in a weird middle ground in that respect - the TTC's streetcars are modern, but no other city operates them, and they run in the street like they have from the beginning.
Chicago has the 'L,' its elevated rapid transit network, which is iconic of that city. I'll be taking a look at it in a future Tunnel Visions post that will appear in early October. Toronto doesn't have anything like it - except the Scarborough RT, portions of which are elevated, like this stretch that bridges McCowan Road. Even then, though, the Vancouver SkyTrain would be a more accurate comparison.
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