It may still feel like summer, but Tuesday, Sept.1 marks the beginning of Colorado’s winter traction season on the I-70 Mountain Corridor. If you travel between the Front Range and the mountains, now is a good time to make sure your vehicle – and your tires – are ready.
Colorado’s chain and traction laws are designed to keep vehicles moving safely when snow and ice hit the high country. And with the following changes that took effect in fall 2025, even drivers with all-wheel drive and four-wheel drive vehicles should take another look at the requirements before heading west.
Here’s what you need to know.
Traction Law vs. Chain Law
You’ll often hear “chain law” used as a catch-all term, but Colorado has several different winter traction requirements.
Passenger Vehicle Traction Law
From Sept.1 through May 31, Colorado’s Passenger Vehicle Traction Law is in effect on the I-70 Mountain Corridor between Morrison and Dotsero. CDOT can also activate traction requirements on other state highways when winter weather and road conditions warrant.
Under the current requirements, a passenger vehicle must have:
- Four-wheel drive or all-wheel drive, plus tires with at least 3/16-inch tread depth that are rated as winter tires, all-weather tires or mud-and-snow tires (look for the mountain/snowflake or M+S designation); OR
- Chains or an approved alternative traction device on at least two drive tires.
That second option is particularly important for drivers of two-wheel-drive vehicles or vehicles that don’t otherwise meet the tire and drivetrain requirements.
And one important change to remember: AWD or 4WD by itself is no longer enough. Your tires also must meet the state’s tread-depth and tire-rating requirements.
Noncompliance can result in a $100 fine plus a $33 surcharge, and fines increase significantly if a vehicle blocks a travel lane.
When Does the Passenger Vehicle Chain Law Apply?
The Passenger Vehicle Chain Law is different – and much more restrictive. CDOT may activate it during severe winter storms as a final safety measure before closing the highway. When a Passenger Vehicle Chain Law is in effect, every vehicle must have chains or an approved alternative traction device, regardless of whether the vehicle has AWD, 4WD or winter tires.
That means having a capable vehicle isn’t necessarily enough to get you through every winter storm. If you regularly travel I-70 during the winter, carrying an approved traction device can provide an important extra layer of preparedness.
What About Commercial Vehicles?
Commercial vehicles have separate requirements. Colorado’s Must Carry Law require commercial motor vehicles with a GVWR or GCWR of at least 16,001 pounds to carry appropriate chains or approved alternative traction devices from Sept.1 through May 31 on designated mountain corridors.
Those routes include I-70 west of Morrison, as well as portions of CO 9, US 40, US 50, US 160, US 285 and US 550.
An Alternative to Traditional Chains: AutoSock
Traditional metal chains aren’t the only option available to passenger vehicles. AutoSock is included on CDOT’s list of approved alternative traction devices. It is a textile traction device that fits over a vehicle’s drive tires to improve traction on snow and ice.
For drivers who don’t routinely install chains, one benefit is its relatively simple installation process. AutoSock’s installation instructions involve three basic steps: pull the AutoSock over the upper portion of the tire, move the vehicle approximately half a wheel turn and then pull the device over the remaining portion of the tire. The device centers itself once the vehicle begins moving.
Before using any traction device, make sure you have the correct size for your tires and understand where it should be installed on your vehicle. It’s also a good idea to practice putting it on before you’re standing alongside I-70 in a snowstorm.
Watch before winter hits:
Watch AutoSock’s step-by-step installation video
Five Things to Do Before Your First Winter Trip
A little preparation at home can make a big difference once you’re on the road.
1. Check your tires.
Look for the mountain/snowflake, M+S or appropriate all-weather designation and make sure your tread depth is at least 3/16 inches. Remember that even AWD and 4WD vehicles now need qualifying tires to comply with the Traction Law.
2. Know whether your vehicle complies.
Don’t assume that AWD, 4WD or a newer vehicle automatically meets Colorado’s requirements.
3. Carry chains or an approved alternative traction device.
Make sure it’s the correct size for your tires and compatible with your vehicle.
4. Learn how to install your traction device before you leave home.
Whether you’re carrying chains or AutoSock, a snowy mountain highway is not the ideal place to read the instructions for the first time.
5. Know before you go.
Check COtrip.org before heading to the mountains for current road conditions, closures and traction or chain law alerts. CDOT also communicates active laws through highway signs and travel alerts. Visit GoI70.com for more information on traveling the I-70 Mountain Corridor.