i used a Dahon Mu SL for the year just like that.
20" with spike (Marathon Winter) tires are as good for winter as any 26" or 700c bikes

which was great, now that trained me well to do the full 45Km (1 way) on my own.
i used to take a mix of bike + train + bike
but i wanted to kill the public transit portion as it was always unreliable, slow, and it was simply a PITA.
so this year i gathered up my balls to do the full ride on my own
and very proud of it, now that it's been 3 month after 90Km a day doesn't seems like that far anymore