In the UK we get the occasional Big Freeze lasting a week or 2 (more further north) with snow, ice, freeze/thaw/freeze action.
I have ridden with 32mm touring tyres without mishap but I didn't like commuting in these conditions. I made some studded tyres (DIY instructions all over the web) and they give me a lot of confidence on the slickest ice.
The commercial versions are not really worthwhile for a week or 2 of extra riding, where there are public transport alternatives. The DIY version costs about $20-30 per pair and takes 2-4hrs of construction. Mine are on their 3rd year of use.