While Toronto does have a lot of traffic, and certainly the suburbs are entirely car-centric... Toronto is ridiculously cold, snowy and icy in winter. Reducing cars on Yonge St (for example) wouldn't make winter go away.
Other than during particular cold snaps or storms, Toronto is VERY far from "ridiculously cold, snowy and icy". Perhaps it's ridÃculosus compared to the tropics, but it's tepid compared to most of canada and much of Europe/Asia.