Colorado Traction Law vs Chain Law: What I-70 Drivers Need

A tire that feels fine on a dry street in Denver can be the wrong tire two exits later, once I-70 climbs into the foothills and the snow starts. Colorado wrote a law about exactly that. Two laws, really, and drivers mix them up every winter.

The traction law sets a minimum for your tires and drivetrain. The chain law is the step CDOT takes when the traction law is no longer enough, and almost every passenger car then needs chains or an approved fabric sock on the tires. Here is what each one asks of you, where it applies, and what it costs to ignore.

What the traction law requires

The rule turns on two questions: what drives your wheels, and how much tread is left. CDOT's traction law decision tree lays it out like this.

Source: Colorado Department of Transportation traction law decision tree.

That 3/16 inch line trips up more drivers than the tire type does. On a tread depth gauge it reads 6/32, three times the 2/32 inch point where NHTSA says a tire should be replaced. So a tire can pass the penny test, stay legal on a dry highway in Denver, and still fail the traction law the moment the signs go up.

AWD helps you get moving. It does nothing for braking on ice. An SUV can climb the Mount Vernon Canyon grade with ease and still need every bit of tread to stop on the way back down.

When the chain law takes over

CDOT calls the chain law in severe storms, and its winter driving page describes it as the final safety measure before a highway closes. Once it is in effect, every vehicle needs chains or an approved alternative traction device on the tires. AWD, new winter tires and deep tread do not change that.

Commercial trucks run under their own chain law with separate stations and heavier fines. If you drive a rig over the hill, that is its own topic. For passenger cars, the practical point is this: if you see chain law signs and you have nothing to put on the tires, the safe call is to stay off that stretch until it lifts.

Where and when it applies on I-70

The passenger traction law is in effect on I-70 from Morrison to Dotsero every year from September 1 to May 31. That covers the whole foothills climb we work every day, from the C-470 interchange through Genesee, El Rancho and Floyd Hill. Outside those dates, or on other state highways, CDOT can still put it into effect when conditions require.

The overhead message boards on I-70 and CDOT's road conditions site will show which law is active. If you are already on the shoulder when the boards change, our I-70 towing page explains how to give dispatch your mile marker and direction so a truck can find you fast.

What it costs to get caught

CDOT lists the penalties on its traction law page. Driving without the required tires or equipment while the law is active carries a $100 fine plus a $33 surcharge. If your vehicle then blocks a travel lane, the fine jumps to $500 plus a $157 surcharge, or $657 in total.

The fine is rarely the expensive part. A car stuck sideways across a lane on a grade means a tow, sometimes a winch-out from the median first, and a closed lane for everyone behind you.

If you slide off anyway

Stay in the vehicle with your seat belt on unless it is unsafe to stay. Turn on your hazards. Call 911 if anyone is hurt or the car is in a travel lane. Then call a tow company that can reach the grade, not one that will dispatch from across the metro.

A car that is stuck but not damaged usually needs a winch-out service, not a tow. Our operators pull it back to the pavement, check that it rolls and steers, and send you on your way if it is safe to drive. If the tires are the reason you slid, the honest advice is to let us take it down the hill rather than try the grade again.

Traction law questions