I used to opine that the fact of winter makes separate bike tracks a sensible idea, even though in conditions without a winter I would prefer wide outside lanes for cycling, for reasons well explained in most vehicular cycling advocacy texts. However, trying to ride to town and back yesterday, I came to add some caveats to this.
Riding on a bike track in winter is ok, if it is in good shape. It is in good shape if it has been ploughed after last snowfall over a couple of centimetres, and traffic in around-freezing conditions hasn't thrown a lot of irregular bits of snow and ice from the road to the bike track. Ploughs have their job cut out for them even clearing the actual road, yet alone the bike tracks, with the result that bike tracks tend to be cleared only after half a day even for quite moderate (and common) cases of snowfall. Brown mush from the road doesn't end up on the bike track if there is at least a metre and a half from the edge of the road to the track, but very often there is no space for this kind of finery.
On the other hand, if there was just a wide outside lane, the wide bit would not be ploghed at first, but bikes would need to ride on the ploghed part of the road, leading to sideways movement of car when passing. In winter, the exact sideways position of any vehicle can be far less accurate than in nice road conditions, so this is dangerous. When the ploughed surface reached the widened part, it wouldn't probably keep clean because of debris thrown there by passing cars.
So actually both solutions as usually practiced are bad in winter. Only bike tracks substantially separated from the road work well, and they need to be cleared of new snow rapidly enough. Fortunately some bike tracks here meet both requirements. Riding into town where horizontal space has always been at a premium is just not very nice.