What does R2 mean on a California chain control?

R2: chains required, except 4wd/awd with snow tires.

Is all-wheel drive enough?

Often, but not always: California's R2 and Washington's "chains required except all-wheel drive" accept it, R3 and "chains required on all vehicles" do not, and Colorado and Wyoming want suitable tires with it.

When is Colorado's Traction Law in effect on I-70?

Between Dotsero and Morrison, from September 1 to May 31, whenever CDOT calls it; COtrip shows when it is in force.

Winter driving

Chain laws by state

Each state says it its own way: California by level, Colorado by law, Oregon and Washington on the sign. What each one asks of a car, and where to check before you go.

Which controls are in force right now: chain controls now and the mountain passes.

California

R1: Chains or snow tires required
R2: Chains required, except 4WD/AWD with snow tires
R3: Chains required on all vehicles

Chain controls go up by area, from a checkpoint where crews turn back vehicles without chains. R3 is rare; the road usually closes first.

Official word: Caltrans QuickMap · Passes: Donner Pass, Echo Summit, Carson Pass, Tejon Pass (the Grapevine), Cajon Pass, Tioga Pass, Sonora Pass, Ebbetts Pass

Colorado

Traction Law (Code 15): Snow, mud-and-snow (M+S) or all-weather tires with at least 3/16" of tread, or four-wheel or all-wheel drive, or chains or an alternative traction device such as AutoSock.
Passenger Vehicle Chain Law (Code 16): Every vehicle must have chains or an alternative traction device such as AutoSock.
Commercial Vehicle Chain Law (Code 18): Commercial vehicles must chain up. It asks nothing of cars.

On I-70 between Dotsero and Morrison the Traction Law applies from September 1 to May 31 whenever conditions call for it; it is also called on other mountain highways.

Official word: COtrip · Passes: Eisenhower Tunnel, Vail Pass, Loveland Pass, Berthoud Pass, Monarch Pass, Wolf Creek Pass, Red Mountain Pass

Wyoming

Chain Law Level 1: Travel restricted to vehicles with tire chains, adequate snow tires, or all-wheel drive.
Chain Law Level 2: Travel restricted to vehicles with tire chains, or all-wheel drive with mud-and-snow or all-weather tires; commercial vehicles must chain at least two drive wheels.

Wind closes Wyoming highways more often than snow: closures to light, high-profile vehicles on I-80 between Laramie and Rawlins are common all winter.

Official word: WYDOT road report · Passes: Sherman Summit, Elk Mountain and Arlington, Teton Pass, Togwotee Pass

Oregon

Carry chains or traction tires: Have chains or traction tires in the vehicle; you may not need to put them on.
Chains required on vehicles towing or single drive axle: Vehicles towing, and those driven by one axle, must chain up.
Chains required, traction tires allowed: Chains on, unless the vehicle (under 10,000 lb) has traction tires.
Chains required on all vehicles: Every vehicle must chain up.

Official word: ODOT TripCheck · Passes: Siskiyou Summit, Santiam Pass, Mount Hood (Government Camp), Willamette Pass, Deadman Pass (Cabbage Hill)

Washington

Traction tires advised: Advice, not a requirement.
Traction tires required: Approved traction tires, or chains.
Chains required except all-wheel drive: Chains on every vehicle except all-wheel drive.
Chains required on all vehicles: Every vehicle must chain up, all-wheel drive included.

Official word: WSDOT mountain pass reports · Passes: Snoqualmie Pass, Stevens Pass, White Pass, Blewett Pass, Chinook Pass

Questions

What does R2 mean on a California chain control?: R2: chains required, except 4wd/awd with snow tires.
Is all-wheel drive enough?: Often, but not always: California's R2 and Washington's "chains required except all-wheel drive" accept it, R3 and "chains required on all vehicles" do not, and Colorado and Wyoming want suitable tires with it.
When is Colorado's Traction Law in effect on I-70?: Between Dotsero and Morrison, from September 1 to May 31, whenever CDOT calls it; COtrip shows when it is in force.