I've heard conditions other than R-1, R-2 and R-3 announced in California. One time, the announcement was, "Only 4WD with chains on all four" are being allowed on I-80. Note this was shortly before the highway closed as 76 inches fell in 24 hours.
One more tip, very basic to Alaskans: Have a survival bag alone. If your car became your tent for a weekend of enforced snow-camping, what you would want to have? Shovel, tow rope, winter gloves, blankets and sleeping bags, food, water, and maybe a stove. And at least a half tank of gas. Always - at least half a tank when on winter roads.
If the car is mostly upright, it makes a very comfortable snow-camping tent. A 4-cylinder car uses only 0.25 gallons per hour so a tank of fuel gives you two days of warmth, even without cycling it on and off. Recline the seats, take a nap. Set the heat to whatever is comfortable. I do that 5-10 nights a year on gonzo road trips, just to make miles, save time, and skip the motel scene every other night.
Most people include food like power bars, cans of corn, etc, that will last a long time. An XGF in Anchorage figured that once it was October, she didn't have to be limited to canned corn. Hagen Daz ice cream bars would be fine in the truck until Spring.
I read about the opposite approach recommended for pilots. If they stash a few Snickers bars in the plane, they will get nibbled long before you crash land in a remote location. But if you stash some dog biscuits in the plane (1) they are made of mostly food-grade stuff and (2) they last forever, and (3) you won't eat them until you really need to.