Idaho Chain Laws: I-90 Mountain Pass Requirements for Truckers

Where Idaho Chain Laws Apply

Idaho chain law is narrow but deadly when ignored. It applies ONLY to commercial motor vehicles over 26,000 lbs GVW on three specific mountain passes. Unlike Oregon, which activates chain requirements statewide, or Colorado, which covers dozens of corridors, Idaho focuses enforcement on the passes where winter crashes actually happen.

I-84 and I-15 do NOT have chain requirements in Idaho. This surprises drivers coming from Oregon, where I-84 has chain zones on Cabbage Hill. The Idaho side of I-84 follows the Snake River valley and does not climb to elevations that require chain enforcement.

Chain Equipment Requirements

Idaho law specifies exactly what counts as legal chains for commercial vehicles:

• Chains required on at least one tire on each side of one drive axle
• If towing a vehicle with brakes, chains also required on at least one axle near the rear of the towed vehicle
• Chain definition: two circular metal loops connected by a minimum of 9 evenly spaced cross-chains across the tread surface
• Cable chains and automatic tire chain devices (like OnSpot) are generally accepted

Exemptions: Logging trucks, tow trucks responding to incidents, and school buses are exempt from chain requirements.

Crash Data: Why Compliance Matters

The numbers from Idaho Transportation Department paint a clear picture of what happens when drivers ignore chain laws on I-90.

Lookout Pass (I-90, Montana Border)

• 101 crashes between October and March over a recent five-year period
• 47% of those crashes involved commercial motor vehicles
• Summit elevation of 4,711 feet with approaches from both sides
• Weather transitions rapidly — conditions at Coeur d’Alene (30 miles west) do not predict conditions at the summit
• The Montana side descends into Mineral County with equally treacherous conditions

Fourth of July Pass (I-90, Between Coeur d’Alene and Kellogg)

• CMVs represent only 19% of traffic on this stretch
• But CMVs account for 24% of all crashes — a 26% overrepresentation
• Lower elevation (3,173 ft) creates a false sense of security
• Black ice conditions are common because temperatures hover near freezing more often than at higher elevations

How to Check Chain Status

Idaho has confirmed DOT API access for real-time conditions. Use these resources:

• Idaho 511: Call 511 or visit 511.idaho.gov for current chain requirements
• Idaho 511 App: Available with truck-specific settings that filter for CMV-relevant alerts
• ITD TripCheck: Real-time camera feeds at key mountain pass locations
• WSDOT coordination: If entering from Washington on I-90, check both Washington and Idaho conditions — Snoqualmie Pass chain status does not predict Lookout Pass conditions

Seasonal Timing

Chain law activation on Idaho I-90 typically runs from October through early April, though early season storms in September and late storms in May are not uncommon at Lookout Pass elevation.

Connecting to Other States

If you are running I-90 across the Northwest, chain laws change at every state line:

• Washington (westbound): Snoqualmie Pass has a 69-mile chain zone (MP 32-101) with $500 fines. Far more aggressive enforcement than Idaho.
• Montana (eastbound): Chain requirements continue over Lookout Pass into Montana. Montana law requires chains or adequate traction devices on mountain passes.
• Oregon (I-84 corridor): Oregon chain law activates statewide, including Cabbage Hill on I-84. More aggressive than Idaho.

Insurance Implications

Winter operations on I-90 increase your risk profile. One jackknifed truck on Lookout Pass can generate claims that blow through Idaho state minimums ($25,000/$50,000/$15,000) in seconds. A multi-vehicle pileup in chain conditions routinely generates six-figure claims.

Most brokers and shippers running Pacific Northwest freight require $1M CSL regardless of state minimums. If you are running I-90 in winter, that is the responsible floor. Call RMS at (208) 800-0640 for a quote that accounts for your actual operating conditions.