Load Limits & Restrictions

Why Seasonal Road Restrictions Exist

In Montana’s rural areas, including Flathead County, roads go through intense freeze-thaw cycles every spring. As temperatures rise, frost deep in the ground melts, leaving the soil underneath wet and spongy. Heavy vehicles can push the road surface down, creating ruts, cracks, and permanent damage. These temporary load limits (often called frost laws) protect the investment in our roads and keep them safe for everyone.

How Weight Limits Work

The limit is measured in pounds per inch of tire width. It tells you the maximum weight your tires can place on the road for each inch of tire tread that touches the ground.

Simple example: If your tire is 10 inches wide and the limit is 350 lbs per inch, your tire can safely carry up to 3,500 lbs (10 × 350). Wider tires spread the weight over more inches, so they can handle a bit more under the same limit. This system is easy to check and protects the road without weighing every axle on the spot.

When Restrictions Are Typically Implemented

Seasonal road restrictions usually begin in late winter or early spring—whenever frost starts leaving the ground—and last until roads firm up, typically by late spring or early summer. Timing varies each year based on weather and is not tied to a fixed calendar date. The Roads & Bridges Department monitors conditions closely and posts updates here.

What Vehicles Are Affected

These limits mainly apply to heavy commercial trucks, semi-trailers, construction equipment, farm machinery, and any vehicle exceeding the posted weight per inch of tire width. Standard passenger cars, light pickup trucks, and most personal vehicles are not affected. If you are hauling a heavy load or driving a commercial vehicle, check the table above and your tire width before traveling restricted roads.