The Color-Coded Route System
Idaho classifies its highways into five color categories, each with different weight allowances for overweight permits. This system is unique to Idaho — no other state uses it.
| Route Color | Max Single Axle | Max Tandem | Max GVW |
|---|---|---|---|
| Yellow | 22,500 lbs | 37,800 lbs | Varies |
| Orange | 24,000 lbs | 37,800 lbs | Varies |
| Green | 25,500 lbs | 40,000 lbs | Varies |
| Blue | 27,000 lbs | 42,500 lbs | Varies |
| Black/Interstate | 20,000 lbs | 34,000 lbs | 105,500 lbs |
Some designated state highways permit loads up to 129,000 lbs GVW with special permits and appropriate axle configurations.
Standard Weight Limits
On interstate highways (Black routes), Idaho follows federal weight limits:
- Single axle: 20,000 lbs
- Tandem axle: 34,000 lbs
- Gross vehicle weight: 80,000 lbs (standard), up to 105,500 lbs with permit
- Bridge formula applies to all axle spacing
Permit Types and Costs
| Permit Type | Cost | Duration |
|---|---|---|
| Annual Oversize | $43 | 1 year |
| Annual Overweight/Oversize | $128 | 1 year + quarterly mileage |
| Single Trip Oversize | $35 | One movement |
| Single Trip Overweight | $50+ | One movement |
| Extra Length | $43 | 1 year |
All permits are available through the Permits4Idaho online portal. Most permits can be self-issued with same-day processing.
Dimension Limits
| Dimension | Standard | With Permit |
|---|---|---|
| Width | 8 ft 6 in | Up to 16 ft |
| Height | 14 ft | Up to 15 ft 6 in |
| Length (single trailer) | 48 ft | Up to 105 ft combination |
| Length (combination) | 75 ft | Up to 115 ft |
How to Apply
- Visit the Permits4Idaho portal at permits4idaho.iplan.io
- Create a carrier account with your USDOT information
- Select permit type based on load dimensions and weight
- Enter route details (the system flags roads that cannot handle your load)
- Pay online — most permits issued same day
- Print and carry permit in vehicle
For loads over 250,000 lbs or requiring engineering analysis, contact ITD at 208-334-8420.
Comparison to Neighboring States
- Oregon: Uses weight-mile tax instead of traditional permits. Charges per mile based on declared weight.
- Montana: Standard 80,000 lb limit on interstates. Higher weights on some state routes but no color-coded system.
- Washington: Standard federal limits. eSNOOPI Pro system for oversize/overweight permits.
The Idaho system actually favors heavy haulers — designated routes with higher weight limits provide a legitimate path for heavy loads that other states do not offer.
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