Missouri Frost Laws & Spring Thaw Limits

How Missouri handles spring thaw

Missouri runs no annual spring-thaw program. MoDOT doesn't declare seasonal frost restrictions on the state system, so at normal legal weight you're generally fine on Missouri highways year-round. The catch is statutory: when thaw of frost or rain leaves a road soft, MoDOT and county engineers may post reduced weight limits (RSMo 304.210, 304.220), and any posted 'X ton' sign on a county road is the legal limit. Watch for local signs on the roads at each end.

Window, reduction, and where to check

• Season: No routine spring-thaw program. MoDOT does not declare annual seasonal frost restrictions on the state system. RSMo 304.210 lets it and county engineers post soft-road limits only when a specific road turns soft.
• Reduction: None as a standing program. When invoked, MoDOT or a county engineer posts a specific reduced limit on the affected road (RSMo 304.210, 304.220), and that posted 'X ton' sign is the limit where it's up.
• Interstates: Exempt from the seasonal reduction
• Find the current order: MoDOT posts no statewide frost map because there's no annual program. On rural county roads in a hard freeze-thaw stretch, check the county road department for any posted soft-road limits and watch for roadside 'X ton' signs, which are the legal limit where posted.
• Overweight penalty: Standard Missouri overweight fine, charged per pound over the limit. There's no separate seasonal penalty. If MoDOT or a county posts a soft-road limit under RSMo 304.210/304.220 and you exceed it, it's cited as an overweight violation on that road.

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