[Aylmer]

I actually just wrote a brief paper on this; we're still transitioning between two different ways of conceiving of transportation and transit planning - on one hand, the technocratic approach (not derogatory, that's just a loose translation from the French terms) and the post-technocratic approach.

The first sees transportation planning as a process of projecting and building infrastructure in a very detached and impartial way. This is still the norm for most routine road projects or service upgrades.
The latter sees transportation planning essentially as a powerful tool for reshaping the city. Though we've seen this since the 70s here and there around North America, it's becoming more and more common with projects whose main goal is more about redefining or shaping the city rather than responding to existing demand.

I tend to agree more with the latter if only because the idea that you can objectively meet demand without creating it has been thoroughly discredited in the past half century through both evidence and experience. However, it's rarely just one or another.

The Hurontario-Main corridor already has enough ridership to justify investment, but perhaps more importantly, it's meant to concentrate development and activity to hopefully create a "critical mass" of urbanity in Mississauga's developing 'downtown' (it'll be a while until I remove those quotation marks).