Chaining up: winter tire chain rules and safety for truck and bus drivers
When chain laws apply, how to chain up safely and why to practice before winter
A jackknifed truck on a mountain pass can close a highway for hours. Often the cause is simple: a driver who tried to climb a snowy grade without chains. That is why mountain states have chain laws for commercial vehicles.
Federal rules also put the burden on drivers. FMCSA requires extreme caution in snow, ice and other hazardous conditions. Drivers must slow down, and stop driving if conditions become too dangerous [1]. This guide covers chain laws in key states and how to chain up safely.
Colorado's chain law
Colorado has some of the strictest rules. From September 1 through May 31, commercial vehicles over 16,000 pounds and buses carrying 16 or more people must carry enough chains on several mountain highways. These include I-70 west of Morrison, U.S. 40, U.S. 50, U.S. 160, U.S. 285, Colorado 9 and all of U.S. 550 [2].
When the chain law is in effect, drivers must chain up. Colorado uses two levels [3]:
- Level 1. When snow covers part of the pavement on an uphill grade. Single drive axle combinations must chain four drive wheels. Other commercial vehicles need snow tires or chains.
- Level 2. When snow covers the whole road on an uphill grade. All commercial vehicles must chain up. Buses chain two drive wheels.
Fines are steep. Not carrying or using chains can cost up to $500 plus a surcharge. If a truck gets stuck and blocks a lane, the fine is $1,000 plus a surcharge [2].
Some devices can be used in place of chains in Colorado, such as automatic chains, wheel sanders and approved textile socks. Cables are allowed only in limited cases [2].
California's chain controls
California posts three levels of chain control on mountain highways [4]:
Comparison compiled by Safety Behind the Wheel Foundation
California chain control levels
| Level | What it means |
|---|---|
| R1 | Chains required on all vehicles except passenger vehicles and light trucks under 6,000 pounds. Those with snow tires on at least two drive wheels may go without chains but must carry them. |
| R2 | Chains or traction devices required on all vehicles except four wheel or all wheel drive vehicles with snow tires on all four wheels. |
| R3 | Chains or traction devices required on all vehicles, with no exceptions. Roads are often closed before this level. |
Source: California Department of Transportation [4]. Heavy trucks have additional chain rules; check Caltrans truck chain requirements.
While chains are required, the speed limit is 25 or 30 mph [4].
Other states
Washington, Oregon, Idaho, Montana, Utah, Nevada and other mountain states have their own chain rules. Some require commercial vehicles to carry chains during set winter months on certain routes. Rules change, so check each state’s transportation website before a winter trip. Call 511 for current road conditions in most states.
Before winter: get ready
- Buy the right chains for your tire size and axle setup. Chains that are too loose can break and damage the truck.
- Inspect them. Look for broken links, worn cross chains and bent hooks. Carry spare links and repair tools.
- Practice. Put them on in your yard or lot in daylight. Time yourself.
- Pack your gear. Gloves, a waterproof kneeling pad, a headlamp, a reflective vest, warning triangles, rubber tensioners and a rain suit.
How to chain up safely
1. Check conditions and chain law status before you reach the grade.
2. Use a designated chain up area if one is available. Otherwise, pull completely off the road, as far right as you can.
3. Never chain up in a traffic lane or on a narrow shoulder next to fast traffic.
4. Turn on hazard lights, set the parking brake and put out warning triangles.
5. Wear a reflective vest and work facing traffic when you can.
6. Lay the chains out, untangled, with hooks facing out.
7. Drape them over the tires, roll forward slowly if needed, then fasten them snug.
8. Drive a short distance, then stop and retighten.
9. Drive slowly. Listen for slapping or clanking, which means a chain is loose or broken.
10. Remove chains in a chain off area once the road is clear. Driving on bare pavement wears chains out fast.
Warning: A driver kneeling beside a truck on a snowy shoulder is hard for others to see and easy to hit. If traffic is passing close and fast, do not get out. Move to a safer spot first, even if it means waiting.
Driving with chains
- Keep speeds low, at or below posted chain limits
- Avoid hard braking, fast starts and sharp turns
- Leave extra space behind the vehicle ahead
- Watch for vehicles sliding back on grades
- Downshift before steep descents. Do not rely on brakes alone
Checklist: winter chain kit
Checklist from Safety Behind the Wheel Foundation
- Correct chains for every drive tire required in the states I run
- Spare links, repair tool and tensioners
- Heavy gloves, kneeling pad and rain gear
- Headlamp and spare batteries
- Reflective vest and three warning triangles
- Food, water and warm clothes in case of a long closure
- I have practiced putting chains on in good weather
Frequently asked questions
Can I just skip a route when chains are required?
Yes, if you can do it safely and legally. Waiting out a storm or taking a lower route is often the best choice. Federal rules require you to stop driving if conditions are too hazardous.
Do automatic chains count?
In many states, yes. Colorado accepts automatic chains as an approved device [2]. Check each state.
Do passenger cars have to chain up too?
Sometimes. Colorado has a traction law for passenger vehicles on I-70, and California’s R2 and R3 levels apply to most cars.
Related articles
Sources and further reading
- 1Electronic Code of Federal Regulations. “49 CFR 392.14: Hazardous conditions; extreme caution.” ecfr.gov/…/section-392.14
- 2Colorado State Patrol. “Chain Law Information.” csp.colorado.gov/…/chain-law-information
- 3Colorado Department of Transportation. “Chain Up Tips for Commercial Vehicles.” codot.gov/…/chainup-tips
- 4California Department of Transportation. “Chain Controls and Chain Installation.” dot.ca.gov/…/chain-controls
This article reflects the safety priorities of commercial vehicle safety and winter driving. It is general education, not legal advice. Chain laws change, so check each state’s transportation agency before you travel. Reviewed November 2026.
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