I'm aware this doesn't ask the original poster's question, but is relevant...
I'm lucky enough to have a second bike, which is a cheap ebay mountain bike. Last winter I found that cycling with the widest (2.1"), knobbiest tyres I had, at the lowest pressure I dared run (1.5 bar, 20psi for my 85kg) and with caution over the worst bits meant that I didn't slip once on ice, snow or slush. And that included cycling miles for work or leisure every single day that it was snowy. I'd certainly happily run anything fairly fat (around 37mm / 1.5") with heavy tread again, rather than get studded tyres for the few days they are needed.
@ma499 - what width touring tyres do you normally use? Are they mostly slick, or do they have substantial grip? Have you tried running at lower pressure on those snowy days?
In fact, my worst problem was rather a fun one - I'd cycle cautiously but confidently where cars and pedestrians were struggling, then put my foot down and try to climb off the bike... even my trainers didn't have a fraction of the grip that my bike tyres did! I did wear a helmet - I don't normally for road riding, but I do when I think I might fall down, such as ice or technical off-road trails.
This post was edited by
08:47pm 29 Nov 2011.