I think it's R3 you're referring to. Usually, they close down 80 and 50 under R3 anyways, except for local traffic.
IIRC, R1 = 2wd with chains, 4wd with snow tires
R2 = 2wd with chains and snow tires, 4wd with chains
R3 = 4wd only, chains required.
I think.