Studded Tire & Chain Rules 2026-27: Idaho, Washington, Oregon, Montana

Last verified: November 1, 2026. States can change these rules, so check the agency links below before you rely on them.

If you drive I-90 between Montana and Seattle, you cross three sets of winter tire rules in one day. The stud season starts on different dates on either side of the Idaho–Washington line, and the chain rules on the passes are not the same everywhere either. Here is what each state says, in plain language, with links to the source.

Stud season at a glance

Idaho — Studs legal: Oct 1 – Apr 30. Out-of-season fine: About $67 (last published by ITD in 2015).
Washington — Studs legal: Nov 1 – Mar 31. Out-of-season fine: $137.
Oregon — Studs legal: Nov 1 – Mar 31. Out-of-season fine: $165.
Montana — Studs legal: Oct 1 – May 31.

Two things to know about these dates:

They can change. WSDOT can extend Washington's removal deadline when conditions warrant, and the Idaho Transportation Board can grant special exemptions from Idaho's dates. Watch for announcements in late March and April.
Washington allows no individual exceptions. That applies to out-of-state drivers too.

The state-line trap

Idaho's stud season opens on October 1. Washington's opens on November 1.

So during October a Coeur d'Alene driver can legally run studs at home and get a $137 ticket in Spokane, about 30 miles west. In spring the same thing happens in reverse: Washington's season ends March 31, but Idaho's runs to April 30. Each state's dates apply while you're driving in that state. If you cross the line regularly, plan around the shorter window.

Traction tires vs. chains: they are not the same thing

This is where most of the confusion lives, especially in Washington.

Washington

An approved traction tire has at least 1/8" of tread and is marked M+S, All Season, or with the mountain/snowflake symbol. Traction tires are legal year-round.
Studded tires do not meet a chain requirement. If the sign says chains, studs don't count.
Pass signs work in levels:
- Traction Tires Advised.
- Traction Tires Required: passenger vehicles need approved traction tires, and vehicles over 10,000 lb GVWR must chain up.
- Chains Required: every vehicle must chain up except AWD and 4WD vehicles under 10,000 lb GVW that have all wheels in gear, approved traction tires, and chains in the vehicle. The fine is up to $500.
- Chains Required on All Vehicles: AWD and 4WD vehicles too.
AWD and 4WD vehicles only get out of a Chains Required sign if they're carrying chains. If you're stopped without them, you can be cited.
Snoqualmie, Stevens, White and Blewett passes all use these levels. Check WSDOT's pass reports before you leave.

Oregon

Traction tires include studded tires, retractable-stud tires, and tires with the mountain/snowflake symbol.
On chain-required routes, passenger vehicles of 10,000 lb GVW or less that aren't towing may use traction tires instead of chains. That isn't the case under a conditional closure that requires chains on all vehicles.
Ignoring a chain sign is a Class C traffic infraction.

Montana

Montana's DOT can require chains year-round in designated chain areas. These include I-90 westbound at Lookout Pass (mile marker 4 to the Idaho line) and US-12 westbound at Lolo Pass.
When chains are required there, the rule applies to vehicles towing a trailer, which must chain the drive wheels of one axle.
AutoSocks are an approved alternative to chains.

Idaho: We could not find a passenger-vehicle chain-carry law on an Idaho Transportation Department page. That doesn't mean chains are optional when conditions turn. Fourth of July Pass and Lookout Pass both see hard winter weather, so carry them anyway.

What the snowflake symbol does and doesn't mean

The three-peak mountain snowflake symbol means the tire passed a standardized snow traction test. It's a useful baseline for snow.

It does not certify how the tire stops on ice. The test measures acceleration on packed snow, not braking on glare ice. That's why a 3PMSF tire and a studded tire are different tools.

A quick pre-trip check

Check tread depth. NHTSA's replacement point is 2/32". With the penny test, put Lincoln's head in upside down; if you can see all of Lincoln's head, your tread is below 2/32" and it's time to replace the tire. For snow, more tread matters. Around 6/32" is a commonly cited minimum for good snow traction.
Check pressure when the tires are cold, meaning parked for three hours or more. Pressure falls as temperatures drop, roughly 1–2 psi for every 10°F. Inflate to the number on your door placard, not the number on the sidewall.
Check the pass report before you leave. WSDOT, Idaho's 511 service and Montana's MDT all publish current conditions.
Carry chains you've practiced fitting. Practice in your driveway, not on the shoulder at Snoqualmie. If your owner's manual says not to use chains, WSP lists approved alternative traction devices.

Sources

Caretier Tires is reader-supported. Some links on this site may be affiliate links; see our disclosure. This guide summarizes public agency information and isn't legal advice.

A good carter checked his wheels before the frost, not after the axle broke.

Studded Tire and Chain Rules: Idaho, Washington, Oregon, and Montana (2026–27)