Recently Lynne and I spent some time in Calgary, Canada. We used only public transport, and found a thriving PT culture in one of the harshest climates and sprawling cities in Canada.
As you can see in this (admittedly poor) photo, taken on a random day, out of peak hour, the Calgary C-Train gets 270000 passengers a day. (compare this with 160000 passengers a day on the west gate freeway)
Why? Not sure, certainly it goes where people want it to, and it runs very regularly - every 3 minutes. Cold and bad weather is certainly not an impediment. Note the highway that runs parallel, with its single car. Calgary has a population density of 1300 people / km^2, compared to San Jose with a population density of 5100 people / km^2; New Ulm with 1500 people / km^2 and Melbourne with 1600 people / km^2.