MileCheckWhat "chains required" means — traction laws explained
When snow and ice hit a mountain pass, state transportation departments post traction and chain requirements that can change within the hour. Here's what the levels mean and how to check before you climb.
What "chains required" means
When a "chains required" restriction is in effect, you must put tire chains — or another approved traction device — on your tires before you continue past the checkpoint. It's not a suggestion; it's enforced, and troopers turn back vehicles without them. The rule kicks in when the roadway is snow-covered or icy enough that ordinary tires can't hold.
R1, R2, R3 and other levels
States use different labels, but the idea is the same — escalating requirements as conditions worsen. California's widely-copied system is a good example: R1 means chains or snow tires are required; R2 means chains are required on all vehicles except four-wheel/all-wheel drive with snow tires on all four wheels; R3 means chains are required on every vehicle, no exceptions. Other states post "traction tires advised," "traction tires required," and "chains required" in a similar ladder.
It changes fast — check before you go
Pass conditions can go from bare pavement to chains-required within an hour as a storm moves in. The requirement you saw this morning may not be the one in effect this afternoon. Always follow the posted signs at the pass, and check the live cameras and DOT reports before you leave — see current mountain pass conditions for Snoqualmie, Donner, and more.
Be ready before the pass
Carry chains that fit your tires whenever you drive a mountain route in winter, and know how to put them on before you need to — the shoulder of a snowy pass in the dark is a bad place to learn. The MileCheck app shows your exact mile marker as you climb, so if you do have to stop, you know precisely where you are.
Know exactly where you are — live
MileCheck shows your nearest mile marker in real time as you drive, plus live DOT alerts and the nearest camera on your route. Free to start, works offline, runs on CarPlay and Android Auto.
Questions, answered
What does "chains required" mean?
It means you must install tire chains or an approved traction device before continuing past the checkpoint. It's enforced, and vehicles without chains are turned back.
What are R1, R2, and R3 chain controls?
In California's system: R1 = chains or snow tires required; R2 = chains required except for 4WD/AWD with snow tires on all four wheels; R3 = chains required on all vehicles with no exceptions. Other states use similar escalating levels.
Do all-wheel-drive cars need chains?
Often not at the lower levels (like R1/R2) if they have snow tires on all four wheels — but at the highest level (R3), chains are required on every vehicle. Always follow the posted restriction, which can change with conditions.
How do I know if chains are required on a pass?
Check the posted signs at the pass, the state DOT's pass report, and the live cameras before you go. See current mountain pass conditions for the pass on your route.