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2024 Idaho Winter/Spring Frost Law Restrictions

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2024 Idaho Winter Frost/spring Thaw Laws and Seasonal Weight Restrictions

During the spring breakup season in Idaho, the official dates of which are subject to annual announcements by the Idaho Transportation Department (ITD), specific regulations known as frost laws are implemented. These regulations are designed to mitigate potential damage to the state’s road infrastructure during the critical period when the frozen ground thaws and becomes susceptible to harm from heavy vehicles. The frost laws typically commence in March and may extend through May. Under these regulations, the weight limits for loads during the frost law period are defined, distinguishing between those traveling on interstate and non-interstate routes. Legal allowable gross loads vary depending on the number of consecutive axles and the distance between any group’s first and last axles. For loads exceeding 79,000 lbs on Interstate routes and 80,000 lbs on non-interstate routes, specific weight limits are applied based on axle configurations, ranging from two to nine axles.

Idaho Overweight Restrictions

The Special Permit Policy during Spring Breakup, as outlined in Rule 39.03.14, specifies the restrictions the Idaho Transportation Department may impose on the state highway system to ensure public safety and prevent road damage. Load restrictions during this period may include a maximum weight limit, axle weight limits, and speed restrictions. Normal overweight special permit limits are suspended on all highways in the area when seasonal load and speed restrictions are imposed. The administration of load limits based on tire sizes considers the manufacturer’s width marked on tubed tires, and tubeless tires are credited for the width of the conventional tubed tires they replace. 

Idaho Oversize Restrictions

Additional restrictions during the frost law period include width limitations on two-lane roads, reducing the maximum allowable width by special permit to 12 feet 6 inches. Speed restrictions are implemented in marked sections of highways with a maximum load, limiting speeds to 30 miles per hour for trucks and buses with a gross weight of 10,000 pounds or more. For vehicles subject to spring breakup weight restrictions, individual axle weight limitations take precedence over the total gross weight of the vehicle combination. Overweight permits may be issued under specific conditions, including minimum tire width, maximum axle weights for single axles, and the issuance of permits solely for nonreducible loads. In adherence to Rule 39.03.14, these regulations are crucial during the spring breakup season to ensure the safe and responsible movement of heavy vehicles, prevent road damage, and uphold public safety.

For information on operating restrictions for state highways posted for spring breakup limits or to check on a route of travel for construction restrictions, etc., go to and the tracking page. It is important for the trucking industry to cooperate and comply with the load and speed limits. If compliance with the load and speed limits are adhered to, the need for future, more restrictive, limits may be alleviated. Excessive violations may lead to the implementation of more restrictive limits.

See also:

Tire chain laws.
Federal bridge formula.

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