Michigan's Truck Speed Limit Has Two Thresholds, One of Them Seasonal
Date Published
Michigan's rule for heavy vehicles is easy to state and easy to get half right, because there are two separate provisions and they operate on different triggers.
The split, and where it stops applying
MCL 257.627 subsection (4) provides that where the posted speed limit is greater than 65 miles per hour, an individual operating a school bus, a truck with a gross weight of 10,000 lb or more, a truck-tractor, or a truck-tractor with a semi-trailer or trailer or a combination of these vehicles, shall not exceed 65 miles per hour on a limited access freeway or a state trunk line highway.
The conditional matters. The restriction bites only where cars are posted above 65 — on Michigan's 70 mile per hour limited access freeway general limit and its 75 mile per hour segments. Where the posted limit is 65 or below, heavy vehicles run the same speed as everyone else, and there is no split at all.
That is different from California, where the truck limit is absolute regardless of posting.
The seasonal drop
Subsection (3) is the provision drivers new to the state miss. An individual operating a truck with a gross weight of 10,000 lb or more, a truck-tractor, a truck-tractor with a semi-trailer or trailer, or a combination of these vehicles shall not exceed 35 miles per hour during the period when reduced loadings are being enforced.
Reduced loadings are the spring thaw restrictions, commonly called frost laws, imposed when saturated subgrade leaves pavement vulnerable. During that period the speed limit for heavy vehicles on affected routes is not a differential off the posted limit; it is a flat 35.
Two different kinds of rule
The two subsections are worth separating in your head. Subsection (4) is a speed rule that depends on what is posted. Subsection (3) is a pavement-protection rule that depends on what the agency has declared, and it produces by far the lower number.
A driver planning a Michigan run in March needs the second one more than the first.