Montana Frost Laws & Spring Thaw Limits

How Montana handles spring thaw

Montana posts real spring thaw limits (MCA 61-10-128), roughly February through May by district. Restricted routes cap axles at 8 tons single and 16 tons tandem or 400 lb per inch of tire width; the weakest routes drop to 7 tons and 14 tons. Overweight fines run a graduated schedule by pounds over (MCA 61-10-145). Counties post their own roads. Dates shift every year, so check MDT's restriction map before each load.

Window, reduction, and where to check

• Season: Spring thaw restrictions run on affected routes roughly February through May, declared by MDT district as roadbeds saturate. The dates move every year and by route, and limits lift as soon as the road firms up.
• Reduction: On restricted routes axles are capped at 8 tons single and 16 tons tandem, or 400 lb per inch of tire width. The most vulnerable routes drop to 7 tons single and 14 tons tandem or 350 lb per inch. Those posted numbers are the hard limit for the route, so read the sign.
• Interstates: Exempt from the seasonal reduction
• Find the current order: MDT posts current load and speed restrictions at mdt.mt.gov/travinfo/restrictions.aspx with an interactive map. Roadside signs mark the start of every posted route, and counties such as Flathead post their own roads separately.
• Overweight penalty: Montana overweight fines run a graduated schedule set by pounds over the limit (MCA 61-10-145): $30 for up to 2,000 lb over, rising through $300 at 12,001 to 14,000 lb and $400 at 14,001 to 16,000 lb, and higher above that. The 10% tolerance in MCA 61-10-144 only lets you reach the first scale.

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