I agree with rhagfo, if you are in black ice (freezing rain) country then park it, SRW or DRW park it.
I have had experience with going over a bridge (overpass) and hitting a patch of black ice while towing and let me assure you... do not know the feeling of "pucker power" until you have experienced a split second jackknife. We were very lucky and recovered because the patch was short and managed to hit dry pavement.
PS: goes without saying do not use cruise control in wet or slippery conditions either.
GPG