Tennessee Bridge Law: Axle Limits and the 41-Foot Kingpin Rule
Tennessee runs the federal numbers — 20,000 single, 34,000 tandem, 80,000 gross, bridge formula — under TCA 55-7-203, and holds a trailer over 48 feet to 41 feet from the kingpin to the midpoint of the rear tandem under 55-7-201. A 10% margin exists but only for specific commodity trucks off the Interstate.
By Avery Schwartz · Former CDL-A driver, 3 years OTR · Updated 2026-09-15
The numbers at a glance
| Limit | TN | Where it comes from |
|---|---|---|
| Gross weight | 80,000 lb | TCA 55-7-203 |
| Single axle | 20,000 lb | TCA 55-7-203 |
| Tandem axle | 34,000 lb | TCA 55-7-203 |
| KPRA / wheelbase | 41 ft, kingpin to midpoint of the two rear axles; 44 ft to rearmost axle if not a tandem | TCA 55-7-201; towed vehicles over 48 ft |
| Bridge formula applies? | Yes — statewide | W = 500(LN/(N−1) + 12N + 36) in 55-7-203; 10% margin for listed commodities off-Interstate only |
Legal limits change and enforcement varies by road. Confirm anything you're betting a ticket on with TDOT / Tennessee Highway Patrol.
How Tennessee applies the bridge law
Tennessee Code 55-7-203 is the weight statute, and it is federal through and through: no axle over 20,000 lb, no tandem group over 34,000 lb, total gross no more than 80,000 lb, and the formula W = 500(LN/(N−1) + 12N + 36) for any group of consecutive axles. The section also grants a 10% margin of error on gross and axle weights — but only for logging, sand, coal, clay, shale, phosphate, solid waste, recovered materials, farm, and machinery trucks, and only on the state highway system outside the Interstate. A van hauling general freight gets no tolerance.
The length statute, 55-7-201, carries the kingpin rule. If the towed vehicle is longer than 48 feet from the point of attachment and the load is not livestock, motor-vehicle parts, or motor vehicles, the distance from the kingpin to a point midway between the two rear axles may not exceed 41 feet. If the rear axles are not a tandem, the statute uses 44 feet to the rearmost axle instead. Measured to the tandem midpoint, this is the same rule as Pennsylvania and North Carolina, and a standard 53-foot van clears it with the tandems in the middle of the rail.
Separately, TDOT's permit office uses a "kingpin" measurement for overlength permits — kingpin to the rear of the trailer or overhang, with 50 feet as the threshold that makes a load overlength. That is a permit measurement, not the 41-foot legal-length rule, and the two get confused constantly. Tennessee Highway Patrol's Commercial Vehicle Enforcement runs fixed scales on I-40, I-24, I-65, I-75, and I-81.
How to slide your tandems for Tennessee
Keep the kingpin-to-tandem-midpoint distance at 41 feet or less, then slide for 34,000 per tandem. Tennessee is a crossroads state — I-40 and I-75 feed Georgia and North Carolina, both 41-foot states, and I-24 feeds Illinois's looser rule — so the 41-foot setting is usually the one to keep for the whole trip.
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 Tennessee 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 Tennessee
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 or gross over 80,000 — the ordinary THP citation; fines are per-pound over. The 10% commodity margin does not apply to general freight.
- Kingpin-to-tandem-midpoint over 41 feet on a trailer over 48 feet, commonly cited with overlength.
- Overlength without a permit on specialty loads where the kingpin-to-rear-of-load measurement exceeds 50 feet; verify with TDOT.
Tennessee bridge law FAQ
What is Tennessee's kingpin-to-rear-axle limit?
41 feet from the kingpin to a point midway between the two rear axles, for towed vehicles over 48 feet (TCA 55-7-201). If the rear axles are not a tandem, 44 feet to the rearmost axle.
Does Tennessee allow a 10% weight tolerance?
Only for specific vehicles — logging, sand, coal, clay, shale, phosphate, solid waste, recovered materials, farm and machinery trucks — and only off the Interstate. General-freight vans get no margin.
Does the bridge formula apply on Tennessee state routes?
Yes. TCA 55-7-203 applies the federal formula to vehicles operated on the public highways of the state generally.
What is TDOT's 50-foot kingpin measurement?
A permit threshold: TDOT measures from the kingpin to the rear of the trailer or overhang, and past 50 feet the load is considered overlength for permit purposes. It is not the 41-foot legal-length rule.
Related
Sources
- TCA 55-7-203 — Maximum weight per axle or group of axles (FindLaw text)
- TCA 55-7-201 — Maximum length of vehicles; 41-ft kingpin rule (FindLaw text)
- TDOT — Oversize/Overweight FAQs (kingpin measurement) (PDF)
- J.J. Keller — U.S. KPRA allowances (Tennessee 41 ft)
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.