Kentucky truck weight limits
On Interstate highways in Kentucky, federal weight limits apply. Four checks decide whether your truck is legal — and the one that surprises most drivers is the Federal Bridge Formula, which can fail a truck that passes every other limit.
Federal limits on Kentucky Interstates
| Limit | Maximum | Applies to |
|---|---|---|
| Single axle | 20,000 lb | Any one axle |
| Tandem axle group | 34,000 lb | Axles 40–96 inches apart |
| Tridem axle group | governed by the bridge formula | 3 axles in a group (no flat federal cap) |
| Gross vehicle weight | 80,000 lb | The whole rig |
| Bridge formula | varies by spacing | Every group of 2+ axles |
The bridge formula check
L is the spacing in feet between the outer axles of a group, N the number of axles. A standard 5-axle rig at 51 ft is capped at 79,500 lb by this formula — under the 80,000 lb gross limit. Full explanation with worked examples.
Kentucky-specific rules
Kentucky rates its highways by class — AAA, AA and A — and the class sets how heavy you can run off the Interstate (603 KAR 5:066). On the Interstate and on Class AAA highways the limits are the standard 20,000 lb single axle, 34,000 lb tandem, 80,000 lb gross, plus the Federal Bridge Formula; Class AA and Class A roads carry lower caps. Kentucky's Appalachian coalfields add a distinctive layer: a designated extended-weight coal haul road system where coal and coal by-products may run up to 90,000 lb (plus a 5% tolerance).
Kentucky exceptions to the federal limits
Kentucky limits by highway class (603 KAR 5:066):
| Measure | Class AAA (and Interstate) | Class AA / A |
|---|---|---|
| Single axle | 20,000 lb | reduced by class |
| Tandem axle group | 34,000 lb | reduced by class |
| Maximum gross | 80,000 lb | reduced by class |
- Coal haul road system (KRS 177.9771): on designated coal or coal-by-product haul roads, gross may reach 90,000 lb with a 5% tolerance for qualifying loads.
- Two consecutive tandem sets may each carry 34,000 lb where the extreme axles are 36 ft or more apart.
- On Interstates, federal limits govern — 20,000 / 34,000 / 80,000 plus the bridge formula.
Seasonal & designated-route rules in Kentucky
Kentucky does not run a statewide spring "frost law" program. The route-level constraints that matter are the highway class (AAA/AA/A) of each road — a lower class means a lower legal weight — and posted-bridge limits, which are common in the eastern mountains and coalfields. Confirm the class and any posting on every non-Interstate segment before running heavy.
Overweight permits in Kentucky
Loads over the class limit need an oversize/overweight permit from the Kentucky Transportation Cabinet (single-trip or annual), route-specific by bridge and pavement rating. The extended-weight coal haul system is a separate designation with its own conditions.
Fines & enforcement in Kentucky
Enforced by the Kentucky State Police and the Transportation Cabinet at fixed weigh stations and with portable/mobile enforcement. Overweight violations carry graduated per-pound penalties; running over a road's class limit is the common way carriers get caught in Kentucky.
What dispatchers should check in Kentucky
- Check the highway class — AAA carries 80,000 lb, but AA and A roads carry less; the class governs your legal weight off the Interstate.
- Coal hauls — the extended-weight coal haul road system allows up to 90,000 lb + 5% on designated roads for qualifying loads only.
- Posted bridges — common in the eastern coalfields; a posting overrides the class limit.
- Interstate — federal 20,000 / 34,000 / 80,000 plus the bridge formula.
Kentucky truck weight — frequently asked questions
How much can a truck weigh in Kentucky?
On Kentucky Interstates the federal gross-weight limit is 80,000 lb, with a 20,000 lb single-axle limit, a 34,000 lb tandem limit and the Federal Bridge Formula. Kentucky sets its own limits on non-Interstate roads — see the Kentucky-specific rules on this page.
Does Kentucky follow federal truck weight limits?
On the Interstate system, yes — federal limits govern in every state. Off the Interstate, Kentucky applies its own axle, gross and permit rules, detailed on this page where they have been verified against the official state source.
What is the single-axle weight limit in Kentucky?
The federal single-axle limit of 20,000 lb applies on Kentucky Interstates. Some states set a different single-axle figure on non-Interstate roads — check the Kentucky-specific section above for the governing number.
What is the maximum tandem-axle weight in Kentucky?
On Kentucky Interstates the federal tandem limit is 34,000 lb. Several states allow a different tandem weight on non-Interstate roads — see the Kentucky exceptions above for the figure that governs.
Scaled heavy in Kentucky?
If the trailer tandems are over, the fix is usually a computed tandem slide, not unloading — see how sliding tandems shifts weight. And here's what an overweight ticket really costs before you decide to run it.
Run your scale-ticket weights through the federal and bridge-formula calculator in your browser. The full platform predicts axle loads from load placement before you load, computes the exact slide-to-legal fix, and applies Kentucky rules on top of the federal baseline.
Open the free calculatorOur calculator runs the federal single, tandem, gross and Bridge Formula checks in seconds. The full platform adds per-state limits, axle-load prediction and the slide-to-legal fix.
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