Michigan Bridge Law: Federal Limits Plus Michigan's Own Axle Rules

Michigan is the state with 164,000-lb gravel trains, but for a five-axle tractor-trailer on the Interstate the rules are federal: 20,000 single, 34,000 tandem, 80,000 gross, bridge formula. Off the Interstate, Michigan uses per-axle limits instead of group limits, and a 53-foot trailer has a wheelbase band it must fall inside.

By Avery Schwartz · Former CDL-A driver, 3 years OTR · Updated 2026-09-15

The numbers at a glance

Limit	MI	Where it comes from
Gross weight	80,000 lb on the Interstate with the federal formula	MCL 257.722(12); higher on state routes with more axles
Single axle	20,000 lb Interstate; 18,000 lb state rule at 9+ ft spacing	MCL 257.722(1), (12)
Tandem axle	34,000 lb Interstate; 16,000/axle (32,000) state rule with 9-ft clearance, else 13,000/axle	MCL 257.722(2), (3), (12)
KPRA / wheelbase	37.5–40.5 ft (±0.5 ft), kingpin to center of rear axle assembly, for semitrailers over 50 ft	MDOT legal loadings guide and J.J. Keller; statute text not confirmed — verify with MDOT
Bridge formula applies?	Yes on the Interstate and designated highways	MCL 257.722(12)

Legal limits change and enforcement varies by road. Confirm anything you're betting a ticket on with MDOT / Michigan State Police.

How Michigan applies the bridge law

Michigan's weight law, MCL 257.722, is famous for what it allows on state roads: an 11-axle combination can legally gross 164,000 lb because Michigan limits weight per axle rather than per group. Subsection (1) allows 18,000 lb on an axle spaced 9 feet or more from its neighbors; subsection (2) allows 16,000 lb per axle on a tandem assembly with no other axle within 9 feet, and 13,000 per axle otherwise; subsection (3) lets a five-axle tractor-semitrailer run two consecutive tandems at 16,000 per axle on designated highways. That is 32,000 on a tandem, not 34,000, under the state rule.

The federal numbers come in through subsection (12): on the Interstate and specially designated highways, a vehicle grossing no more than 80,000 lb may run 20,000 on a single axle, 34,000 on a tandem, and the federal bridge formula for any group of consecutive axles. For a standard 80,000-lb van on I-94, I-75, I-96, or I-69, that is the set you plan on. MDOT's "Maximum Legal Truck Loadings and Dimensions" guide lays out both systems side by side.

Length is where Michigan is strange. MCL 257.719 allows a 53-foot semitrailer with no overall length limit, but MDOT's loadings guide and J.J. Keller's KPRA table both describe a wheelbase requirement for semitrailers longer than 50 feet: 37.5 to 40.5 feet, plus or minus 0.5 foot, measured from the kingpin to the center of the rear axle or rear axle assembly. We could not confirm that band in the statute text we retrieved, so treat it as MDOT guidance and verify before relying on it. Read literally, it is a band, not just a cap — tandems slid too far forward can be out of it as easily as too far back.

How to slide your tandems for Michigan

On the Interstate, slide for the federal 34,000 tandem limit, then check that the kingpin-to-tandem-center distance lands inside 37 to 41 feet under MDOT's guidance. Most 53-foot vans hit that band somewhere in the middle of the rail; the ends of the rail are where you get in trouble in both directions.

Worked example. You scale at the first CAT after the shipper: steer 11,800, drives 35,300, trailer tandems 31,900, gross 79,000. Gross is legal; the drives are 1,300 over. Sliding the tandems forward (toward the cab) moves weight from the drives to the trailer axles. On a trailer with 4-inch hole spacing, a hole is worth roughly 250 lb, so 1,300 lb needs six holes: drives about 33,800, tandems about 33,400. Both groups are under 34,000 with a few hundred pounds of margin, and the gross hasn't changed. Now check the geometry for Michigan using the row in the table above — and if you'll cross into a stricter state, set for that one instead. The Tandem Slide Calculator does the hole math for your trailer's actual rail spacing and tells you which direction to move.

Common tickets in Michigan

Based on the statutes above and what drivers commonly report; citation practice varies by officer and county, so treat this as a watch list, not a fine schedule.

Tandem over 34,000 on the Interstate or per-axle over 16,000 on a state route — Michigan State Police Commercial Vehicle Enforcement runs fixed scales on I-94 and I-75 and heavy portable-scale activity around Detroit and Grand Rapids.
Frost-law violations — Michigan reduces legal axle weights on many roads during spring thaw; watch for posted seasonal restrictions from roughly March to May.
Wheelbase / kingpin outside the MDOT band on a trailer over 50 feet, less common but reported; verify the current rule with MDOT.

Michigan bridge law FAQ

Is Michigan's tandem limit 32,000 or 34,000?

34,000 lb on the Interstate and designated highways under MCL 257.722(12). Under Michigan's per-axle state rule, a tandem is 16,000 per axle — 32,000 — with a 9-foot clearance requirement, or 13,000 per axle without it.

Does Michigan have a kingpin-to-rear-axle rule?

MDOT and J.J. Keller describe a wheelbase band of 37.5 to 40.5 feet (±0.5 ft) from the kingpin to the center of the rear axle assembly for semitrailers longer than 50 feet. We could not confirm the exact text in MCL 257.719; verify with MDOT.

How does Michigan allow 164,000 lb if the federal limit is 80,000?

Michigan's per-axle rules predate the federal limits and are grandfathered on non-Interstate roads. The 80,000-lb federal cap and bridge formula apply on the Interstate; heavier combinations run on designated state routes.

What are Michigan frost laws?

Seasonal reductions in legal axle weight (commonly stated as 25–35%) during the spring thaw on posted roads. They change year to year; check MDOT and county road commission notices.

Sources

This page is a driver's summary, not legal advice. Statutes are quoted or paraphrased from the sources listed; where we couldn't verify a figure from an official source we've said so.