This recent Spacing article by Geoff Turnbull and Laurence Holland makes a compelling case for "missing middle" type development along Toronto's collector roads. The idea being that we are already focusing on (and have policies for) infill along our Avenues and within our single family neighborhoods, but we have yet to pay attention to the scale of street that sits somewhere in between the two. Streets such as Hallam that were once commercial spines, but lost their economic purpose for a variety of reasons.

Here's a map, from the article, of Toronto's collector roads:

There are almost 800 kilometers of collector roads in the city. As the name starts to imply, these streets are designed to collect vehicles and funnel them toward arterial roads and "Avenues." But this scale difference changes things and creates a kind of in-between condition. They're less desirable from a residential standpoint (because they're not as quiet and secluded), but they're also not designed to become strong retail/commercial streets (despite the odd retail remnant). In fact, retail is probably prohibited on most. Which is why I like the idea of thinking of these streets differently.

Of course, we have work to do in order to make this scale of development economically feasible, and the authors do acknowledge that. But the more we continue to talk about the future of our low-rise neighborhoods, the more that intensification starts to feel inevitable.