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Status update, October 21, 2026.
- The traction law season runs September 1 to May 31 on I-70 between Morrison and Dotsero, and CDOT can turn the law on for any state highway. When it's on, an AWD or 4WD car needs all-weather, M+S or winter tires with at least 3/16-inch tread. Any car that doesn't meet that, including a 2WD car, needs chains or an approved traction device on two or more drive tires. A ticket costs $100 plus a $33 surcharge, or $500 plus $157 if your car ends up blocking a lane (CDOT, CDOT).
- Independence Pass (CO 82 between Aspen and Twin Lakes) is still open (Independence Pass Foundation). CDOT says it typically closes on or near November 7 (CDOT); it closed on November 17 in 2025 and on October 31 in 2024. Cottonwood Pass west of Buena Vista usually closes in late October or early November, and Guanella Pass around Thanksgiving (Denver Gazette). Check COtrip.org the morning you drive.
What the law requires
Colorado's Passenger Vehicle Traction Law covers cars, SUVs and light trucks under 16,001 pounds. It's in place every year from September 1 to May 31 on I-70 between Dotsero (mile 133, east of Glenwood Springs) and Morrison (mile 259, just west of Denver), and drivers have to comply whenever overhead signs say it's active. CDOT can also activate it on any other state highway when conditions call for it, and announces it on road signs, COtrip.org and 511. (Colorado State Patrol, CDOT)
When the law is active:
- 4WD and AWD vehicles need tires with at least 3/16-inch tread that are rated mountain-snowflake, M+S (also written M/S or M&S) or all-weather. If the tires don't qualify, the car needs chains or an approved alternative traction device (ATD) on at least two drive tires.
- 2WD vehicles need chains or an approved ATD installed on at least two drive tires. Good tires alone no longer count for 2WD (more below).
Which tires count
Look at the tire sidewall. You want one of these markings:
- The three-peak mountain snowflake symbol (a dedicated winter tire, or some all-weather tires).
- M+S, M/S or M&S (mud and snow). Many all-season tires carry this.
- An all-weather rating from the manufacturer.
The tread also has to be at least 3/16 of an inch deep, so a worn tire with the right marking can still fail. If you aren't sure, a tire shop can measure the tread in seconds.
The 2WD chain rule
A 2025 law, SB25-069, took away the tires-only option for two-wheel-drive vehicles. The Colorado State Patrol now says 2WD vehicles on the covered stretch of I-70 must carry chains or an approved ATD from September 1 to May 31, whatever tires they have. When the traction law is active, the chains or ATD have to be on at least two drive tires. Upgrading to M+S or winter tires doesn't make a 2WD car compliant. (Colorado State Patrol, Colorado General Assembly)
CDOT keeps a list of approved ATDs, which includes fabric "tire socks" such as AutoSock and several cable-chain products (CDOT). For a winter mountain trip, that makes an AWD or 4WD rental the simpler choice.
Traction law vs. chain law
The Passenger Vehicle Chain Law is the next step up. CDOT uses it in severe storms as the last measure before closing the road. When it's in effect, every passenger vehicle needs chains or an approved ATD, including 4WD and AWD cars with good tires. Commercial trucks have their own chain law, and on several mountain routes they have to carry chains all season. (CDOT, Colorado State Patrol)
Fines
Official sources don't all list the same amounts, so plan for the higher figures:
- CDOT's traction law page lists a $100 fine plus a $33 surcharge for not complying. CDOT's November 2025 announcement cited $50 plus a $17 surcharge.
- If a non-compliant vehicle causes a lane closure, CDOT lists up to $500 plus a $157 surcharge. The State Patrol lists up to $500 plus $79 for winter-restriction violations, and $1,000 plus $157 if you're stuck and blocking the road.
(CDOT, CDOT news release, Colorado State Patrol)
Checking a rental car
If you drive a rental, the law applies to you as the driver. Before you leave the lot:
- Ask for AWD or 4WD if you're going into the mountains between September and May. Book that category specifically rather than "SUV or similar." Our Colorado car rental guide covers what to book.
- Read the sidewalls for the mountain-snowflake, M+S or all-weather marking, and look at the tread depth.
- If you end up with 2WD, you need chains or an ATD with you on the covered stretch of I-70. Read your rental agreement on chains before you buy any.
- Check COtrip.org for active traction or chain laws and closures before you set out.
Beating I-70 traffic
I-70 climbs through Idaho Springs to the Eisenhower-Johnson Memorial Tunnel at more than 11,000 feet. On winter weekends, much of the Front Range drives to the same few ski areas at the same time. These habits help:
- Head west before about 6 a.m. on weekends, or ski on weekdays.
- Come back early (leave the mountain by about 1-2 p.m.) or late (after dinner). The eastbound slowdown on Saturday and Sunday afternoons is the worst of the week.
- The tolled Mountain Express Lane between Empire and Idaho Springs can save time when it's open.
- After a big storm, everything takes longer. Leave extra time and fill up the tank before you climb.
Pack a basic winter kit: a scraper, a warm layer and gloves, water and snacks, a phone charger, and a blanket in case you're stuck in a closure.
Skip the drive
Shared and private shuttles run from DEN and Denver to the ski towns, guided day tours handle I-70 for you, and state buses and the Winter Park Express train run in ski season. See our Breckenridge and Vail shuttle guide, airport ski shuttles, winter day tours and ski resorts near Denver.
Frequently asked questions
When is the Colorado traction law in effect?
It's in place every year from September 1 to May 31 on I-70 between Dotsero and Morrison, and drivers must comply whenever signs say it's active. CDOT can also activate it on any state highway when conditions call for it.
Do all-season tires meet the Colorado traction law?
On a 4WD or AWD vehicle, yes, if the tires are marked M+S (or M/S) and have at least 3/16-inch tread. On a 2WD vehicle, no. Since a 2025 law change, 2WD vehicles need chains or an approved traction device whatever tires they have.
What is the fine for breaking the traction law?
CDOT lists a $100 fine plus a $33 surcharge, though an earlier CDOT release cited $50 plus $17. If you block the road, it can rise to $500 or more, and the State Patrol lists up to $1,000 plus a $157 surcharge.
What is the difference between the traction law and the chain law?
Under the traction law, AWD and 4WD vehicles can rely on qualifying tires. The chain law is used in severe storms, and under it every vehicle needs chains or an approved traction device.
Does the traction law apply in Rocky Mountain National Park?
The park can enforce Colorado's traction law. When it's active there, vehicles need properly rated tires with at least 3/16-inch tread or an approved traction device.
Sources are linked in the text. We check them when we update the page, but rules, dates and prices change, so confirm with the official source before you go.