Idaho Frost Laws & Spring Thaw Limits

How Idaho handles spring thaw

Idaho runs a real program. ITD posts spring breakup limits (Idaho Code 40-312) roughly late February into May, cutting posted state-highway sections to 16,000, 14,000, or 12,000 lb per axle by severity, with a 30 mph cap on rigs rated 10,000 lb or heavier. Highway districts post their own signs on county roads. Sections change year to year and week to week, so pull the current order at 511.idaho.gov before you load.

Window, reduction, and where to check

• Season: Spring breakup season, roughly late February into May, declared by ITD section by section as frost leaves the ground. The dates shift every year and restrictions flip on and off as temperatures swing, so this is not a fixed calendar.
• Reduction: Posted sections drop to one of three axle caps set by how bad the breakup is: 16,000 lb, 14,000 lb, or 12,000 lb on any axle. Trucks and buses rated 10,000 lb GVWR or heavier also get a 30 mph speed cap on posted sections.
• Interstates: Exempt from the seasonal reduction
• Find the current order: ITD posts current spring breakup restrictions at 511.idaho.gov and on its highway restrictions map. A red marker means the 30 mph limit and reduced axle caps are active, yellow means resume the posted speed, green means the section is open to legal loads. Check the morning of the trip.
• Overweight penalty: Standard Idaho overweight schedule (Idaho Code 49-1013): graduated from $5 for the first 1,000 lb over, up to $2,500 plus $0.30 per pound once you top 20,000 lb over the seasonal limit.

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