Illinois Frost Laws & Spring Thaw Limits

How Illinois handles spring thaw

Illinois runs no statewide spring-thaw program on state highways. The restrictions are local: city and county agencies may post reduced weight limits for up to 90 days when thaw or rain would damage a road (625 ILCS 5/15-316), and the limit isn't legal until the sign goes up. Mostly you'll see it in the northern counties in March. The roadside 'X ton' sign is the law, so check the local road authority for both ends.

Window, reduction, and where to check

• Season: No statewide IDOT spring-thaw program. Local city and county road agencies post seasonal restrictions, mostly in the northern half of the state, typically starting around March and set by local weather. Roads and dates vary by jurisdiction and shift each year.
• Reduction: No fixed statewide percentage. Under 625 ILCS 5/15-316 a local authority may post a reduced limit for up to 90 days when thaw or rain would damage a road, usually a signed 'X ton' or per-axle cap. The restriction isn't legal until the sign is up, and the sign is the limit.
• Interstates: Exempt from the seasonal reduction
• Find the current order: IDOT doesn't post frost restrictions on state highways, so check the county highway department and city public works for the local roads at each end. The roadside seasonal sign controls.
• Overweight penalty: Illinois overweight schedule (625 ILCS 5/15-113): $100 up to 2,000 lb over, jumping to about $270 at 2,001-2,500 over and climbing steeply from there. A posted local frost limit is enforced as an overweight violation.

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