Streetcars are also exceedingly useful for peripheral circulation in large metropolitan areas. Basically, an underground is most suitable for the most heavily built-up areas, but you can then carry a lot of traffic on streetcar lines which serve medium density areas around or on the fringes of the subway area. Munich & Toronto both do this effectively (although more lines are desperately needed in both cities).
Helsinki is another place which co-ordinates streetcars with subways. Also the northernmost subway in the world, which I have ridden ― by apparently about 50 km compared to that of Petrograd! Not, however, the most northerly electric street railway, which is elsewhere in Finland, & which I have not ridden.
basically, the cost of a subway and the optimal ridership is so high that in many cases, street-level transit like light rail/trams/streetcars is better.
wrt toronto, our city is on a grid layout and the main subway lines are north-south and east-west, so it is easy for streetcar and bus routes to feed into the subway lines.
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