A sure sign of spring, potholes are the result of fluctuating temperatures and vehicle traffic on roads. (Graham Jaehnig/Daily Mining Gazette)

HOUGHTON — An annual rite of spring, seasonal road restrictions in Keweenaw, Houghton, Baraga and Ontonagon counties took effect on March 3.

The following Monday, the Michigan Dept. of Transportation imposed its weight restrictions on all state trunkline highways for the entire state of Michigan, both Upper and Lower Peninsulas.

County road commissions and city public works departments put in place their own seasonal weight restrictions, which usually, but not always, coincide with state highway weight restrictions.

According to michigan.gov, on routes designated as “Seasonal” (solid or dashed red on the MDOT Truck Operators Map) there will be a weight reduction of 25% for rigid pavements and 35% for flexible pavements.

In the Copper Country, restrictions call for a 35% reduction.

On March 9, Moody Market reported road restrictions in downstate Van Buren County were also in effect. Road restrictions there are similar to the U.P’s.

“Heavy trucks need to be 35% less of their capacity weight because right now,” Van Buren County Road Commission Managing Director Bret Witkowski is quoted by Mooody Market as saying. “You’ve got the moisture from the thaw coming through the road, and this is when there can be a lot of damage, and obviously, heavy vehicles cause a lot of that damage,”

According to the County Road Association of Michigan, (CRA) seasonal weight restrictions allow county road agencies to regulate the speed limit and the amount of weight trucks carry to reduce damage to roads.

While concrete and asphalt surfaced roads look indestructible, the CRA says, they can actually be quite fragile in late winter as frost comes out of the ground. Even strong late-winter sunlight on the dark paved surface has a significant impact on a road.

As frost melts beneath a paved road, the roadbed turns wet and spongy, because water is trapped between the pavement and the remaining ice layer beneath. When trucks and heavy equipment travel over a layer of concrete or asphalt that is not well supported beneath, lots of permanent cracks can occur.

When temperatures drop, the water that has infiltrated the cracks freezes and expands. This expansion puts pressure on the surrounding pavement. When temperatures rise and the ice melts, the water contracts, creating gaps.

The weight of vehicles passing over the road exerts pressure on weakened areas. Repeated stress can cause the surface to crack further. When snow and ice melt, trapped moisture beneath the road makes it more susceptible to damage.

County Road Association of Michigan states one of the most common business interactions with a county road agency concerns seasonal weight restrictions – sometimes called “frost laws.”

On state trunk lines, MDOT determines when weight restrictions begin each spring by measuring frost depths along state highways, observing road conditions, and monitoring weather forecasts. Weight restrictions remain in effect until the frost line is deep enough to allow moisture to escape and the roadbeds regain stability.