Motor carrier classes by state
Michigan does not tell a dump operator what his truck may gross. It tells him what each axle may carry, and lets him add axles — except on the Interstates and designated highways, where a second and entirely different rulebook takes over at 80,000 pounds. Which rulebook applies is a function of the road, not the load.
The exposures that make dump and aggregate work its own insurance class — the tight duty cycle, the loading and placement sites that are not roads, the overhead strikes and rollovers that dominate the severity — are the same in Michigan as anywhere, and they are covered on the dump trucking insurance page rather than restated here.
Michigan’s contribution is a weight code unlike any other state’s. Section 722 of the Michigan Vehicle Code prices capacity per axle and names no gross ceiling at all in its opening subsections: 18,000 pounds where axle spacing is 9 feet or more, 13,000 pounds where spacing is less than 9 feet but more than 3-1/2 feet, and 9,000 pounds where axles are spaced less than 3-1/2 feet apart. The statute calls that set the normal loading maximum. Add axles at legal spacing and the arithmetic keeps going, because nothing in those subsections stops it.
Then subsection (12) of the same section says its own loading maximum applies to interstate highways, and to highways the state transportation department or a local authority designates, and on those it imposes the federal bridge formula, a 20,000-pound single axle, a 34,000-pound tandem and a hard 80,000-pound gross. One vehicle code, two irreconcilable capacity models, separated by which road the truck is on. That is the fact that shapes a Michigan aggregate operation, and it is the fact most often reported wrongly.
Every figure below is tied to the subsection or bulletin that sets it, with the effective date of the version quoted. The weight text here is Michigan Compiled Laws complete through Public Act 20 of 2026; section 722 was last amended by 2024 Public Act 106, effective April 2, 2025. The seasonal figures are from the 2026 restriction season.
Running mixed all-season and seasonal routes out of a Michigan pit? Send the route classification alongside the equipment list — in this state the road decides which weight rule the truck is under.
MCL 257.722, subsection (1), sets the maximum axle load by the distance between axles: 18,000 pounds if the spacing is 9 feet or more between axles for vehicles equipped with high pressure pneumatic or balloon tires; 13,000 pounds if the spacing is less than 9 feet between 2 axles but more than 3-1/2 feet; and 9,000 pounds per axle if the axles are spaced less than 3-1/2 feet apart. Subdivision (d) names those three together as the normal loading maximum.
Subsections (2) and (3) then let the state transportation department, or a local authority for roads under its jurisdiction, designate highways where bridges and road surfaces are adequate for heavier loading, on which a tandem axle assembly may run at up to 16,000 pounds per axle where no other axle sits within 9 feet. On a truck tractor and semitrailer with not more than 5 axles, two consecutive tandem assemblies may run at that figure on designated highways.
Nowhere in subsections (1) through (3) is there a gross vehicle weight ceiling. That absence is the whole point of the Michigan configuration: capacity is bought by adding legally spaced axles, which is why Michigan aggregate trailers carry axle counts that look extraordinary to an operator from any neighboring state. The much-quoted ceiling that circulates on trucking forums is an arithmetic consequence of counting axles at those spacings — it is not a number that appears in section 722, and quoting it as a statutory allowance is the most common error made about this state.
Subsection (12) is the counterweight, and it opens by stating that the loading maximum in that subsection applies to interstate highways, alongside highways the department or a local authority designates. On those roads the limits are 20,000 pounds on any 1 axle including all enforcement tolerances, a tandem axle weight of 34,000 pounds including all enforcement tolerances, the bridge formula W = 500 [(LN)/(N-1) + 12N + 36], and a gross vehicle weight that must not exceed 80,000 pounds including all enforcement tolerances. Whether the axle-count model reaches the Interstate System is a genuinely contested reading, and no operator should plan a haul on the assumption that it does.
Federal law caps Interstate weights but preserves what states already allowed when the cap arrived. For almost every state the preserved baseline is what was in effect on July 1, 1956. Michigan has its own line in the statute.
Title 23 of the United States Code, section 127, at subsection (a)(7), provides that with respect to the State of Michigan, laws or regulations in effect on May 1, 1982 shall be applicable for the purposes of that subsection. It is a named state with a named date, a quarter century later than the general rule, and it is the reason the Michigan axle model survived a federal weight framework that otherwise flattened state variation.
The practical significance for an aggregate hauler is one of interpretation rather than of arithmetic. The grandfather preserves Michigan law as it stood on a specific date; it does not itself grant a weight. What weight it preserves, and how far onto the Interstate System that reaches, is settled by reading MCL 257.722 rather than by reading the federal section — and MCL 257.722(12) is unambiguous that its own limits, including the 80,000-pound gross, apply to interstate highways.
For underwriting, the useful takeaway is that a Michigan configuration is not portable. A trailer built to exploit the axle-spacing model is a Michigan asset with limited value in an adjacent state, and an operator who buys Michigan iron and then wins work in Ohio or Indiana has bought a scheduling problem along with the equipment. That shows up on the physical damage schedule as a valuation question long before it shows up as a claim.
Most states that restrict for thaw post a tonnage. Michigan reduces by proportion, which means the cut lands hardest on the operators who were carrying the most. MCL 257.722(8) provides that during the months of March, April and May in each year, the maximum axle load allowable on concrete pavements or pavements with a concrete base is reduced by 25% from the maximum axle load specified in the chapter, and the maximum axle loads allowable on all other types of roads during those months are reduced by 35%.
The same subsection cuts the wheel load in parallel. During the period the seasonal road restrictions are in effect the maximum wheel load must not exceed 525 pounds per inch of tire width on concrete and concrete base, or 450 pounds per inch of tire width on all other roads. Read that against subsection (7), which sets the normal maximum wheel load at 700 pounds per inch of width of tire, and the seasonal wheel figures are the same 25% and 35% cuts expressed on a different measure.
Because the reduction is proportional rather than absolute, it interacts with the axle-count model in a way a tonnage posting would not. An operator running a high-axle-count configuration loses a percentage of every axle, so the absolute tonnage he gives up in March is larger than the tonnage a lighter competitor gives up — the constraint scales with the asset. That is the opposite of how a posted five-ton or seven-ton restriction behaves in a state that uses one.
Subsection (8) also imposes a publication duty that is useful to a dispatcher. The state transportation department and each local authority with roads under its jurisdiction to which the seasonal restrictions apply must post, on the homepage of its website or on the website of a statewide road association where the local authority has no site of its own, both the dates when the seasonal restrictions are in effect and the names of the highways and streets and portions of highways and streets to which they apply.
We place Michigan aggregate, sand and gravel accounts across tandem, tri-axle and multi-axle train configurations, including operators running both all-season and seasonal routes out of the same pit.
Michigan does not divide itself into numbered thaw zones and post a table of dates. It classifies individual routes, and then moves a geographic boundary across the state in staged bulletins. The classification is published on the MDOT Truck Operators Map, and the bulletins state the effect in the map’s own colors: on routes designated as all-season routes, green or gold on the map, there is no reduction in legal axle weight; on routes designated as seasonal, solid or dashed red on the map, there is a weight reduction of 25% for rigid pavements and 35% for flexible pavements.
That is a different planning problem from a zone table. Two pits fifteen miles apart can sit on opposite sides of the classification, and a single haul can begin on an all-season trunkline and finish on a seasonal county road, with the load legal for the first half of the trip and over for the second. The route classification, not the county, is the unit of analysis.
The 2026 season shows how the staging works. MDOT’s spring weight restriction bulletins opened the season with Bulletin #1, effective 6:00 p.m. on Tuesday, February 17, 2026, imposing restrictions on state trunkline highways from the Indiana and Ohio border north to and including US-10 in Ludington in Mason County, then east to US-127 in Clare County, north on US-127 to M-61, and east on M-61 to the intersection of US-23 in Standish, Arenac County. Seven further bulletins advanced and then withdrew that line, and Bulletin #8, effective 7 a.m. on Friday, May 15, 2026, lifted the remaining seasonal weight restrictions on all state trunkline highways statewide.
The statute makes the months indicative rather than binding. MCL 257.722(10) allows the state transportation department, or a local authority for highways under its jurisdiction, to suspend the restrictions imposed by the section when and where conditions of the highways or the public health, safety and welfare warrant suspension, and to impose the restricted loading requirements on designated highways at any other time that the conditions of the highway require. A Michigan restriction season is therefore a declared season that usually falls inside March, April and May, not a season the calendar guarantees.
Michigan has a length allowance that exists for one kind of equipment, and it is unusual enough to be worth reading carefully. MCL 257.719, at subsection (2)(f), sets the general limit for a truck tractor, semitrailer and trailer, or a truck tractor and 2 semitrailers, at 59 feet.
Subsection (2)(g) raises that to 65 feet for a truck tractor, semitrailer and trailer, or a truck tractor and 2 semitrailers, in which no semitrailer or trailer is more than 28-1/2 feet long — but only while the vehicle is being used for a business purpose reasonably related to picking up or delivering a load, and only if each semitrailer or trailer is equipped with a device or system capable of mechanically dumping construction materials or dumping construction materials by force of gravity.
Three conditions therefore travel together: the per-unit length, the business purpose, and a dumping mechanism on every trailing unit. It is rare for a length statute to describe a body type at all, and rarer still for it to condition the allowance on the equipment being capable of the work. A Michigan operator running that configuration has an allowance that a general freight carrier with identical dimensions does not.
Michigan writes its permit rules around this kind of work as well. MCL 257.725, at subsection (11), provides for an annual permit for the movement of construction equipment issued to a power unit, without requiring a separate permit for each individual piece of equipment carried by that power unit; the state transportation department fee for that permit is $264.00 under subsection (4), against $50.00 for an ordinary single trip and $100.00 for multiple trips or an annual permit. Subsection (12), added by a 2018 amendatory act, further provides that such a permit may be presented on a mobile device, may not restrict daily operating hours, may include only Memorial Day weekend, the Fourth of July holiday and Labor Day weekend as restricted holidays, and may not require travel more than 10 miles per hour below the posted speed limit.
The insurance consequences follow the configuration rather than the statute. A trailing unit that dumps is a unit with hydraulics, a raised-body exposure and an overturn profile of its own, and it belongs on the schedule as a rated unit rather than as an attachment. Where those units are pulled behind equipment the insured does not own, or dropped with another party, the interchange question needs answering — that is trailer interchange territory, and it is regularly missed on multi-unit dump combinations because the trailers look like part of one vehicle.
The exemption catalog in section 722 is long, and reading it is the fastest way to see where a gravel hauler stands. Subsection (5) exempts a person hauling agricultural commodities from the seasonal reductions on notice to the county road commission not less than 48 hours before the pickup or delivery. Subsection (6) exempts public utility vehicles under emergency and nonemergency conditions with their own notice regimes. Subsection (9) allows exemptions for milk on specified routes when requested in writing, with approval or denial within 30 days. Subsection (8) itself carves out school buses and a propane delivery to a residence where the vehicle’s propane tank is filled to not more than 50% of capacity and the vehicle travels at not more than 35 miles per hour. Subsection (13) grants a 10% axle increase for agricultural commodities or raw timber from the place of harvest or farm storage to the first point of delivery, expressly not on an interstate highway and expressly not on a road subject to seasonal restrictions while they are in effect.
Aggregate appears on none of those lists. That is the structural fact underneath the questions asked at submission:
The answers to those five tell an underwriter whether the operator is running the calendar or being run by it. In a state where the reduction is proportional, the operator with the most capacity has the most to lose in March, and the account that has planned for that reads very differently from the one that has not.
Two coverages carry more weight here than the class average would suggest. A compressed and route-dependent operating pattern concentrates payroll into fewer weeks and into harder conditions, which is a workers compensation question about seasonal hiring and training as much as a rating exercise. And where an operator pivots to other work during restrictions — demolition debris, contaminated soil, millings — the material change may outrun the policy, which is where a pollution liability review belongs.
The state minimum is a licensing threshold. The program an operator actually needs is built from these lines:
We write dump and aggregate hauling as a named class rather than as an exception to general trucking, and we read each account against the weight and permit regime of the state it operates in. For a Michigan operator that means starting from what the trucks are actually licensed and configured to carry, sizing physical damage to bodies and hoists rather than to a chassis value, and treating pit, stockpile and job-site work as its own exposure rather than an extension of the highway auto form.
If the operation also runs freight under separate authority, the Michigan trucking insurance page covers the state’s broader motor carrier picture, and the dump trucking insurance page covers the class mechanics that apply wherever the operator runs.
MCL 257.722(1) sets it by spacing: 18,000 pounds where the axle spacing is 9 feet or more, 13,000 pounds where the spacing is less than 9 feet but more than 3-1/2 feet, and 9,000 pounds per axle where axles are spaced less than 3-1/2 feet apart. Subdivision (d) names those three together as the normal loading maximum. Subsections (2) and (3) allow up to 16,000 pounds per axle on a tandem assembly on highways the department or a local authority designates as adequate.
Not in the opening subsections, and that is the source of most confusion about this state. MCL 257.722(1) through (3) state axle maximums with no gross ceiling attached. But subsection (12) applies its own limits to interstate highways and to designated highways, and those include a 20,000-pound single axle, a 34,000-pound tandem, the federal bridge formula and a gross vehicle weight that must not exceed 80,000 pounds including all enforcement tolerances.
By percentage rather than to a fixed tonnage. MCL 257.722(8) reduces the maximum axle load by 25% on concrete pavements or pavements with a concrete base and by 35% on all other types of roads during March, April and May. The maximum wheel load during restrictions is 525 pounds per inch of tire width on concrete and concrete base and 450 pounds per inch on all other roads, against a normal maximum of 700 pounds per inch under subsection (7).
It is a route classification published on the MDOT Truck Operators Map, and it decides whether the seasonal cut applies at all. MDOT’s spring weight restriction bulletins state that on routes designated all-season, green or gold on the map, there is no reduction in legal axle weight, while on routes designated seasonal, solid or dashed red on the map, there is a weight reduction of 25% for rigid pavements and 35% for flexible pavements. A single haul can cross from one to the other.
MDOT Bulletin #1 imposed restrictions effective 6:00 p.m. on Tuesday, February 17, 2026, on state trunkline highways from the Indiana and Ohio border north to and including US-10 in Ludington, then east to US-127 in Clare County, north to M-61 and east to US-23 at Standish. Seven further bulletins staged the line northward, and Bulletin #8, effective 7 a.m. on Friday, May 15, 2026, lifted the remaining seasonal weight restrictions on all state trunkline highways statewide.
No. MCL 257.722(8) names those three months, but subsection (10) lets the state transportation department, or a local authority for highways under its jurisdiction, suspend the restrictions when and where conditions of the highways or the public health, safety and welfare warrant it, and impose the restricted loading requirements on designated highways at any other time that highway conditions require. The 2026 season in fact began in February, before the statutory months opened.
Because Congress named it. Title 23 of the United States Code, section 127(a)(7) provides that with respect to the State of Michigan, laws or regulations in effect on May 1, 1982 shall be applicable for the purposes of that subsection, in place of the July 1, 1956 baseline that governs most states. It preserves the state’s own weight framework as it stood on that date; it does not itself grant any particular weight, which is settled by reading MCL 257.722.
MCL 257.719(2)(g) permits a truck tractor with a semitrailer and trailer, or with 2 semitrailers, to reach 65 feet where no semitrailer or trailer is more than 28-1/2 feet long, against the 59-foot general limit in subsection (2)(f). It applies only while the vehicle is used for a business purpose reasonably related to picking up or delivering a load, and only if each trailing unit is equipped with a device or system capable of mechanically dumping construction materials or dumping them by force of gravity.
Every figure on this page was read at the source below on August 11, 2026, with the effective date of the version read. Treat each as current as of that date rather than as permanent.
Send the declared or registered weights alongside the axle configurations, and tell us where the material moves from. We will size the program against the work the trucks actually do rather than against a statutory floor.
