Anything under 4km is walking distance. Over 4 would be biking distance.
When I lived downtown Toronto I often walked from Bloor/Spadina to Yonge/Bloor.
Now that I'm in the suburbs I walk to the GO train. Everyone else on my street that takes the GO train drives, and it's literally an 8-10 minute walk to the station. An SUV, two minivans and two cars all drive by me in the morning. In the evening, I walk by them as they're stuck in the traffic trying to leave the parking lot

It's faster to walk but people still prefer to drive.
I've tried commuting by car years ago and I hated every single day of it. I shudder just when I think about it. Stuck in traffic for hours because some idiot was in a rush and caused an accident, stuck in traffic because people living in country where it snows every year cannot handle few inches of snow (they don't need winter tires either, it never snows or gets cold in Canada

), stuck in traffic because of road repairs... blah...
edit: Got carried away and forgot the thread's about biking. I lived in Ottawa for few years and I used to bike everywhere, during winter as well, but the distances were much shorter than the ones I'd have to cover living in GTA. Didn't even feel a need for a car, bike + car rentals + public transit was good enough.