What is the Colorado Traction Law?
Colorado's Traction Law (CDOT Code 15) is a winter driving rule the Colorado Department of Transportation activates on a highway when snow or ice makes it necessary. While it is active, every passenger vehicle must have tires with at least 3/16 inch of tread plus either M+S or winter-rated tires, or four-wheel or all-wheel drive, or carry chains or an approved alternative traction device. If conditions get worse, CDOT can step up to the Passenger Vehicle Chain Law (Code 16), which requires chains or an alternative traction device on every vehicle.
Most winter closures on I-70 are not caused by the snow itself. They are caused by a few cars that spin out on a grade and block every lane behind them. The Traction Law exists to keep those cars off the mountain on the days that matter.
This guide covers what the two laws require, how to tell whether your tires pass, how the I-70 mountain corridor is handled from fall through spring, and where to look before you leave Denver.
Two levels
Code 15 And Code 16,
In Plain Language
Traction Law (Code 15)
This is the first level and the one you will see most often. Your vehicle is compliant if it has at least 3/16 inch of tread and one of the following: tires marked M+S (mud and snow), tires with the mountain-and-snowflake winter symbol, or four-wheel or all-wheel drive. A two-wheel-drive car with worn or summer tires can still drive legally if it carries chains or an approved alternative traction device, such as a fabric tire sock, and installs them.
Passenger Vehicle Chain Law (Code 16)
This is the last step before CDOT closes a road. When it is active, every passenger vehicle needs chains or an approved alternative traction device, and four-wheel or all-wheel drive alone does not satisfy it. In practice, the Chain Law is used sparingly and usually on specific passes during the worst of a storm. If you see it posted and you do not have chains, the safe choice is to wait it out.
Commercial vehicles are separate
Trucks have their own chain requirements on I-70 and other mountain routes, which is why you will see chain-up stations along the corridor. Those rules do not change what a passenger car needs, but they are a useful signal: if the trucks are chaining up, conditions are serious.
The corridor everyone drives
I-70 From Morrison
To Dotsero
Since 2019, Colorado law has treated the I-70 mountain corridor between Morrison and Dotsero as a seasonal traction zone from September 1 through May 31. CDOT still activates the Traction Law there, and on other highways, whenever conditions call for it. The practical rule for visitors is simple: between fall and late spring, make sure your car would pass before you head west on I-70, even if the forecast in Denver looks clear.
The corridor climbs to more than 11,000 feet at the Eisenhower-Johnson Memorial Tunnel and crosses Vail Pass at 10,662 feet. Weather at the tunnel can be completely different from weather in Golden an hour earlier. Storms also tend to arrive on Friday afternoons and Sunday afternoons, when ski traffic is heaviest, which is when a single stuck car causes the longest delays.
Drivers who are not compliant while the law is active can be fined, and the penalty is higher if a noncompliant vehicle ends up blocking the road. The bigger cost is usually time: a spinout on a grade can stop traffic for hours.
Before you leave
A Five-Minute
Winter Check
- Read the sidewall. Look for M+S, M/S or the mountain-and-snowflake symbol. All-season tires on most cars carry an M+S rating.
- Measure the tread. An inexpensive tread-depth gauge from any auto parts store tells you whether you have 3/16 inch. If you are close to the line, assume you are below it.
- Check COtrip. CDOT posts active Traction Law and Chain Law codes, closures and cameras on COtrip.org and in the COtrip app. Inside Colorado you can also dial 511.
- Pack for a stop. Warm layers, water, snacks, a phone charger, a scraper and a full tank. Closures on I-70 can last hours, and the tunnel area is cold even when the road is moving.
- Leave early or late. Driving outside the weekend ski rush lowers the odds of being stuck behind a spinout.
Going further than the Front Range? Our Colorado scenic byways guide lists which high routes close for the season, and the best time to visit Colorado explains what each month looks like on the roads.
Keep planning
- Things to do in Colorado — places to go once you get over the pass.
- Best time to visit Colorado — month by month, including mud season.
- Colorado scenic byways — routes, surfaces and seasonal closures.
- COtrip.org — CDOT's official road conditions, closures and active traction codes.
Common questions
Winter Driving Questions,
Answered Plainly
What tires meet Colorado's Traction Law?
Tires with at least 3/16 inch of tread that are also rated M+S (mud and snow), carry the mountain-and-snowflake winter symbol, or are mounted on a four-wheel-drive or all-wheel-drive vehicle. A two-wheel-drive car without those tires needs chains or an approved alternative traction device such as a fabric tire sock.
Is four-wheel drive enough in Colorado?
Under the Traction Law, four-wheel drive or all-wheel drive with at least 3/16 inch of tread is compliant. Under the Passenger Vehicle Chain Law, the next and stricter step, it is not: every vehicle then needs chains or an approved alternative traction device, regardless of drivetrain.
Where can I check if the Traction Law is active?
The Colorado Department of Transportation posts active Traction Law and Chain Law codes on COtrip.org and in the COtrip app, and on overhead message signs along I-70 and other mountain highways. You can also dial 511 inside Colorado for road conditions.
Do rental cars in Colorado meet the Traction Law?
Not automatically. Many rental cars have all-season M+S tires, but tread depth and drivetrain vary. Check the tire sidewall for M+S or the snowflake symbol, ask the counter for an all-wheel-drive vehicle if you are heading into the mountains, and read the rental agreement before buying chains, since some agreements restrict their use.
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