Basics
R-1 vs R-2 vs R-3: California chain control levels explained
Live chain control
Updated · Caltrans / NDOT data via Snowy Roads, refreshed every 3 minutes. Tap a chip for checkpoints, cameras and signs.
R-1: chains required unless you have snow-tread tires. R-2: chains required unless you drive a 4WD or AWD vehicle with snow-tread tires on all four wheels. R-3: chains on every vehicle, no exceptions. Under R-1 and R-2 you must still carry chains. Today's I-80 and US-50 levels are shown above.
R-1: chains required except with snow tires
Caltrans' wording: chains are required on all vehicles except passenger vehicles and light-duty trucks under 6,000 pounds gross weight and equipped with snow tires on at least two drive wheels. Chains must be carried by vehicles using snow tires.
In plain terms, R-1 is the mild level. A car with snow-tread tires keeps driving; a car on summer tires or worn all-seasons without an M+S marking puts chains on. Vehicles towing trailers need chains on one drive axle, and trailers with brakes need chains on at least one axle. R-1 often appears first as a storm starts and last as it clears.
R-2: chains required except 4WD or AWD with snow tires
Caltrans' wording: chains or traction devices are required on all vehicles except four-wheel-drive and all-wheel-drive vehicles with snow-tread tires on all four wheels. Four-wheel and all-wheel-drive vehicles must carry traction devices in chain control areas.
R-2 is the level you will see most during a real storm. Two-wheel-drive cars chain up even if they have snow tires. 4WD and AWD vehicles continue only if all four tires are snow-tread, and they must have chains in the car.
R-3: chains required on all vehicles
Caltrans' wording: chains or traction devices are required on all vehicles, no exceptions.
Every vehicle chains up, including 4WD and AWD on snow tires. R-3 is rare because the highway is often closed before conditions get that bad; when you do see it, expect very slow travel and a closure to follow.
Quick comparison
| Your vehicle | R-1 | R-2 | R-3 |
|---|---|---|---|
| 2WD, tires without an M+S marking | Chains | Chains | Chains |
| 2WD with snow-tread tires (under 6,000 lb) | No chains, carry them | Chains | Chains |
| 4WD or AWD, tires without an M+S marking | Chains | Chains | Chains |
| 4WD or AWD with snow-tread tires on all four wheels | No chains, carry them | No chains, carry them | Chains |
| Anything towing a trailer | Chains on one drive axle | Chains on one drive axle | Chains |
What counts as a snow-tread tire
Caltrans uses the California Vehicle Code definition: a snow-tread tire has a relatively deep and aggressive tread pattern compared with a conventional passenger tire, and can be identified by the letters MS, M/S, M+S or the words MUD AND SNOW stamped into the sidewall. Tires with the three-peak mountain snowflake symbol are a stricter category and always qualify. Most all-season tires carry an M+S marking; summer tires do not. Check your own sidewalls before the season rather than at the checkpoint, and read chains for AWD, 4WD and snow tires if you are unsure what your car needs.
Every restriction code you may see
Chain control signs, QuickMap and Snowy Roads use a wider set of codes than R-1 to R-3. The truck codes mostly show up on I-80 over Donner Summit.
| Code | Meaning |
|---|---|
| R-0 | No chain controls are in effect at this time. |
| R-1 | Chains required on all vehicles except passenger vehicles and light-duty trucks under 6,000 lb with snow-tread tires on at least two drive wheels; snow-tire vehicles must carry chains. |
| R-1 MODIFIED | Trucks and vehicles pulling trailers require chains, traction devices or snow tires on the drive axle; passenger vehicles are not affected. |
| R-2 | Chains or traction devices required on all vehicles except 4WD/AWD vehicles with snow-tread tires on all four wheels; 4WD/AWD must carry chains. |
| R-3 | Chains or traction devices required on all vehicles, no exceptions. |
| ESC | The California Highway Patrol is escorting all traffic because of weather conditions. |
| TH | All truck-trailer combinations are being held at the chain control checkpoint because of incidents or weather. |
| TS | All trucks must stop at the chain checkpoint; Caltrans is screening for chains. Trucks without maximum chains are turned around and permit loads are prohibited over the summit. |
| TTA | All truck-trailer combinations are being turned around at the checkpoint because of traction problems over Donner Summit. |
| TTS | All single-axle-drive trucks pulling a trailer are being turned around because of traction problems over Donner Summit. |
| TTSD | All single-axle-drive trucks pulling a set of doubles are being turned around because of traction problems over Donner Summit. |
| VM | Traffic is being metered at the chain checkpoint to reduce congestion in the mountains. |
| HT | All traffic is being held at the chain control checkpoint because of incidents or weather. |
| MIN | Truck chain requirements are at minimum for all trucks using Donner Summit. |
| MAX | Truck chain requirements are at maximum for all trucks using Donner Summit. |
| W | No restrictions; watch for snow on the pavement. |
| RC / Road Closed | Closed to traffic. |
| Not Reported | Condition not reported. |
How the level is posted and enforced
Caltrans decides the level for each stretch of highway and posts it on roadside signs and message boards, on QuickMap (quickmap.dot.ca.gov) and on the highway information line, 1-800-427-7623. Snowy Roads reads the same Caltrans and NDOT data every 3 minutes and shows the level at every checkpoint on the I-80, US-50, SR-88 and US-395 pages. About a mile past the sign, CHP or Caltrans staff check vehicles at the checkpoint and turn around anyone who does not meet the requirement. Levels change without notice as the storm develops, so the level you saw at breakfast may not be the one at the checkpoint. Always carry chains.
FAQ
What is the difference between R-1 and R-2?
Under R-1 any vehicle with snow-tread tires on its drive wheels is exempt from chains. Under R-2 only 4WD and AWD vehicles with snow-tread tires on all four wheels are exempt. Both levels require exempt vehicles to carry chains.
Does R-2 mean I need chains with AWD?
Not if all four tires are snow-tread tires (M+S, M/S, MS or the mountain snowflake symbol). You must have chains in the vehicle. AWD on tires without that marking needs chains under R-2.
How often is R-3 actually posted?
Rarely. Caltrans usually closes the road for spinouts, whiteout or avalanche control before it reaches R-3, so most drivers only ever meet R-1 and R-2.
What is R-1 Modified?
A truck-only version of R-1: trucks and vehicles pulling trailers need chains, traction devices or snow tires on the drive axle, while passenger vehicles are unaffected.
What do the TS and TTA codes mean?
They are truck screening codes used mainly on I-80 over Donner Summit. TS means every truck must stop at the checkpoint and show maximum chains; TTA means truck-trailer combinations are being turned around because of traction problems.
Do the levels mean the same thing in Nevada?
Nevada DOT posts its own requirements on its side of the state line, worded as chains or snow tires required rather than R-1 to R-3. Snowy Roads shows those segments with the NDOT wording.