Are double semitrailers OK in Michigan?
I'm not exactly sure what you saw, Lynn, but double trailers are allowed if hauled by a tractor trailer, the so-called big rigs.
Michigan law limits a truck to hauling no more than one trailer or semitrailer, and a truck tractor to one semitrailer and one trailer in combination at a time. A combination of vehicles cannot exceed 11 axles, except with a special permit. (Michigan Laws 257.719)
So, what is the difference?
Section 59 of Michigan Laws 257.59 defines "semi-trailer" as "every vehicle with or without motive power, other than a pole-trailer, designed for carrying persons or property and for being drawn by a motor vehicle and so constructed that some part of its weight and that of its load rests upon or is carried by another vehicle."
A truck tractor is defined in Section 77 of Michigan law 257.77 as "every motor vehicle designed and used primarily for drawing other vehicles, and not so constructed as to carry a load other than a part of the weight of the vehicle and load so drawn, except that a truck tractor and semitrailer engaged in the transportation of automobiles may transport motor vehicles on part of the power unit."
By the way, Michigan law limits the length of semitrailers to 50 feet, and the truck and semitrailer or trailer to 59 feet. Laws in other states vary.
Three axles have been allowed in Michigan since 2002.