How do I know if I need chains? Where to check chain control

Check whether a chain control is posted on your route, then match the level to your vehicle. Caltrans posts R-1, R-2 and R-3 on roadside signs, on QuickMap and on 1-800-427-7623; the strip above shows what is in effect right now on the main Sierra highways.

Step 1: is a chain control in effect on your route?

Chain controls apply to specific stretches of highway, not to a region, so the question is always "is one posted between me and where I am going?" There are four ways to find out:

• Snowy Roads. Each highway and resort page, for example I-80, US-50, SR-88, US-395 or Palisades Tahoe, lists every Caltrans checkpoint on the way with its current level, the message signs and the cameras, refreshed every 3 minutes from Caltrans and NDOT data. The iOS app adds a per-vehicle answer and alerts.
• Caltrans QuickMap (quickmap.dot.ca.gov). The official live map. Turn on the chain control layer to see the posted stretches.
• The Caltrans highway information line, 1-800-427-7623. Enter the route number and hear the current conditions read out.
• The signs. Once you are driving, roadside "Chains Required" signs with the level, and the overhead message boards, are the final word.

Step 2: match the level to your vehicle

• R-1: chains required unless you have snow-tread tires (M+S, M/S, MS or the mountain snowflake symbol) on the drive wheels of a passenger vehicle or light truck under 6,000 pounds. Carry chains anyway.
• R-2: chains required unless you drive a 4WD or AWD vehicle with snow-tread tires on all four wheels. Carry chains anyway.
• R-3: chains required on every vehicle.

The full definitions and the truck codes are in R-1 vs R-2 vs R-3 explained, and the AWD and snow-tire cases in chains for AWD, 4WD and snow tires.

Step 3: watch for the checkpoint

Chain controls are enforced. Roughly a mile after the "Chains Required" sign there is a checkpoint where CHP or Caltrans staff look at your tires, ask about chains and turn around vehicles that do not meet the requirement. That mile is where you pull fully off to the right and put chains on if you need them. The control ends at an "End Chain Control" sign, after which you take them off at a pull-out. Speed under chain control is 25 or 30 mph as posted.

Where chains are required in California right now

The live strip at the top of this page shows the main corridors. For the rest, each Snowy Roads page carries its own status:

• North Lake Tahoe and Reno: I-80 over Donner Pass; SR-89 and SR-267 around the lake.
• South Lake Tahoe: US-50 over Echo Summit.
• Kirkwood: SR-88 over Carson Pass.
• Mammoth and June Lake: US-395 and SR-203.
• Bear Valley and Dodge Ridge: SR-4 and SR-108.
• Yosemite: SR-120, SR-140 and SR-49, plus the park's own controls inside the entrance.
• Big Bear and Mountain High: SR-18, SR-330, SR-38 and SR-2, on the Big Bear and Mountain High pages.
• Mt. Shasta: I-5.
• Nevada: Mt. Rose Highway and US-50 from Carson City are posted by the Nevada DOT (nvroads.com, 511).

Reading the signs and boards

A message board reading "R-2 CHAIN CONTROL 3 MI AHEAD" means the control starts three miles on, at the level named. "CHAINS REQUIRED" on a static sign with a flip panel showing R-1, R-2 or R-3 marks the start of the control area. Truck-only codes such as TS or TTA on I-80 do not apply to cars. "END CHAIN CONTROL" marks where you may remove chains. When a board says the road is closed or that traffic is being held, no level applies: nobody is going through until Caltrans reopens it.

Timing

Controls go up when snow sticks to the pavement and come down when plows and traffic have cleared it. They are most likely during a storm, overnight after it and in the early morning when melt refreezes, and they change without notice. Check once the night before, once before you leave, and trust the signs over anything you read earlier. Always carry chains in winter, whatever the forecast says.