Colorado's Traction Law: What It Asks of a Boulder Driver

Published 10 October 2026

Boulder Towing Company gets the same call every time the first real storm lands: a car is sideways on a canyon road, and the driver wants to know if the sign that said TRACTION LAW applied to them. It did. The rule is short, but it changed in 2025, and most of what people repeat about it is a version or two out of date.

Below is what the statute says, what the Colorado Department of Transportation (CDOT) and the Colorado State Patrol say it means for a passenger car today, where around Boulder it can be switched on, and what we see at the roadside when a car does not meet it. We leave out the fine amounts on purpose: the published figures do not agree with each other, and the equipment is the part you can do something about.

The traction law is not a stand-alone act. It sits in subsection (5) of C.R.S. 42-4-106, the same section that lets CDOT close a state highway. That subsection gives the department two powers: it may close any portion of a state highway during dangerous driving conditions, and when a road is icy or snow-packed it may restrict travel to vehicles that are properly equipped.

The statute defines its own terms. "Equipped" means the vehicle uses or carries the appropriate traction equipment. "Tire chains" are metal chains with two circular loops, one on each side of the tire, joined by at least nine evenly spaced cross chains. An "alternate traction device" is one CDOT has approved as giving traction comparable to chains or tire cables.

It also says when a restriction starts: once signs are up, and the statute counts temporary and electronic signs. CDOT adds that drivers are told through highway signage, COtrip.org and road condition alerts. From that point, going on without the equipment is unlawful.

CDOT's passenger vehicle page, updated in fall 2025, lists what every motorist needs while a traction law is active. The tread figure is the same in every tire option: 3/16 of an inch.

• AWD or 4WD with mud and snow tires. Marked with the mountain-snowflake icon, M+S or M/S, at 3/16-inch tread.
• AWD or 4WD with winter tires. Same markings, same tread depth.
• AWD or 4WD with tires the manufacturer rates all-weather. Again at 3/16-inch tread.
• Chains or an approved alternative traction device. The one option open to any drivetrain.

Read CDOT's list again and every tire option starts with AWD or 4WD. That is the change. The Colorado State Patrol's chain law page attributes it to Senate Bill 25-069 and puts it bluntly: there is no tire-only option for a two-wheel-drive vehicle under the updated law. Good winter tires on a front-wheel-drive sedan are still a sound idea, but by the Patrol's reading they no longer satisfy the rule by themselves.

The Patrol's summary covers passenger vehicles under 16,001 pounds. On Interstate 70 between Dotsero at milepost 133 and Morrison at milepost 259, it says a two-wheel-drive vehicle must carry chains or an approved device from September 1 through May 31, whatever tires it wears, and must fit them to two or more drive tires when the law is activated. The statute names that same stretch and those same dates.

An AWD or 4WD vehicle keeps its choice: rated tires at 3/16 of an inch, or chains or a device on two or more drive tires. All-wheel drive helps a car get moving; it does not shorten a stop or stand in for tread. It also changes the tow afterward, which is why an all-wheel-drive car rides on a flatbed.

The I-70 corridor is the stretch written into the statute, and it is where most Boulder drivers meet the rule on a ski day. It is not the only place. CDOT states that it can implement traction and chain laws on any state highway. Boulder Canyon is CO 119 and the road to Denver is US 36, so the same sign can light up much closer to home.

One step above the traction law is the passenger vehicle chain law. CDOT uses it in severe storms and calls it the final safety measure before the highway is closed. Under it the drivetrain no longer matters: CDOT says every vehicle must have chains or an approved alternative traction device, and the Patrol specifies two or more drive tires on two-, four- and all-wheel-drive vehicles alike.

After that comes the closure itself, under the same subsection. A closed canyon is closed to everyone, and the statute makes driving past the closure unlawful.

CDOT's winter FAQ describes these as secondary offenses: a driver can be cited when they crash or cause traffic delays and are not compliant. The statute adds an enhanced penalty when a violation closes a travel lane. In practice that means the law reaches a driver at the same moment we do, with the car across a lane or off the shoulder.

The cars we pull out in the first storms tend to share a short list of causes: worn all-season tires, winter tires on one axle only, which CDOT's FAQ says reduces their effectiveness, and chains still in the box because nobody had fitted them in a dry driveway first. Check tread on all four tires before the season, and practice with whatever device you carry.

If the car is already stuck, stay belted in with the hazards on if traffic is passing, and tell us the road, the nearest mile marker and the drivetrain. We handle getting a stuck car winched back onto the pavement and tow it if it cannot drive away. Boulder Towing Company dispatches tow trucks day and night, and we will give you the price and the arrival window on the phone before a truck is sent.