Bridge Law by State: Kingpin Limits and Axle Weights
Federal law sets the floor — 20,000 on a single, 34,000 on a tandem, 80,000 gross, and the bridge formula — but each state decides how far back your tandems can sit on a 53-foot trailer. This hub explains the formula and links to a driver's page for each of the twelve states that matter most.
By Avery Schwartz · Former CDL-A driver, 3 years OTR · Updated 2026-09-15
The federal bridge formula, in one paragraph
W is the maximum weight in pounds on any group of two or more consecutive axles, rounded to the nearest 500. L is the distance in feet between the outer axles of that group. N is the number of axles in the group. The formula exists because a bridge feels concentrated weight, not total weight: 80,000 lb spread over 51 feet of axles is fine, the same 80,000 bunched onto axles standing close together is not. It applies to every group of consecutive axles on the truck — drives alone, trailer tandems alone, drives plus tandems, and steer through last axle — and the strictest group wins.
Three overrides ride on top of it. A single axle never exceeds 20,000 lb. A tandem (two axles more than 40 inches and no more than 96 inches apart) never exceeds 34,000 lb. And two consecutive tandems may each carry 34,000 lb only if the distance from the first axle of the first tandem to the last axle of the second is at least 36 feet — the 36-foot rule that bites when you slide your tandems all the way forward. On the Interstate these come from 23 U.S.C. 127; most states have copied them into their own codes so they apply on state routes too.
Worked example: your drives and trailer tandems together are four axles (N = 4) with 35 feet between the first drive axle and the last trailer axle (L = 35). W = 500 × (35 × 4 / 3 + 48 + 36) = 500 × (46.67 + 84) = 65,333, rounded to 65,500. Even though each tandem is legal at 34,000, the four-axle group can only carry 65,500 — not 68,000 — until you get the span to 36 feet. Run your own spans in the Bridge Formula Calculator.
Why state pages matter: kingpin-to-rear-axle (KPRA)
Weight is federal; geometry is state. Because the STAA of 1982 stopped states from capping the overall length of tractor-trailers, many of them capped something else instead: the distance from the kingpin to the rear axle of the trailer, which controls how wide the rig swings in a turn. That number is the difference between a legal load and a citation at a state line, and it changes what tandem hole you can use — sliding forward to satisfy California's 40-foot limit moves weight onto your drives, which may have been at 33,900 already. Every state page below gives you the KPRA rule, how it's measured (to the rearmost axle or the center of the tandem — they differ by about two feet), and a worked slide example.
The twelve states, side by side
| State | KPRA / wheelbase for a 53-ft trailer | Tandem (lb) | Gross (lb) |
|---|---|---|---|
| California | 40 ft to rearmost axle (38 ft single axle) | 34,000 | 80,000 |
| Texas | None found (semitrailer up to 59 ft) | 34,000 | 80,000 |
| Florida | 41 ft to center of rear axle group | 34,000 Interstate; higher off-Interstate | 80,000 |
| Illinois | 45 ft 6 in to center of rear axle (Class I/II) | 34,000 | 80,000 |
| Georgia | None found — verify with Georgia DPS | 34,000 Interstate; 37,340–40,680 state routes | 80,000 |
| Pennsylvania | 41 ft to centerline of rear axle group | 34,000 | 80,000 |
| Ohio | None in statute — verify with ODOT | 34,000 | 80,000 |
| New York | 43 ft to centerline of rear axle | 34,000 Interstate; 36,000 state rule | 80,000 |
| Michigan | 37.5–40.5 ft (±0.5) to center of rear axle assembly, per MDOT | 34,000 Interstate; 32,000 state rule | 80,000 |
| Indiana | 43 ft to rearmost axle | 34,000 | 80,000 |
| North Carolina | 41 ft to rearmost axle or tandem midpoint | 34,000 Interstate; 38,000 state statute | 80,000 |
| Tennessee | 41 ft to tandem midpoint (44 ft non-tandem) | 34,000 | 80,000 |
All twelve states apply the federal bridge formula on the Interstate; most have adopted it statewide. "None found" means we could not locate a KPRA limit in the state's statute or DOT guidance — see the state page for sources. Figures verified 2026-09-15; statutes change, so confirm with the state DOT before you rely on a number.
Reading the table
Rearmost axle vs. tandem center. California (40 ft) and Indiana (43 ft) measure to the rearmost axle. Florida, Pennsylvania, New York, North Carolina, Tennessee, and Illinois measure to the center of the tandem or rear axle group. Since a standard tandem is about four feet axle-to-axle, 41 feet to center is roughly 43 feet to the rear axle — so Indiana's 43 and the eastern 41s are effectively the same setting, while California's 40-to-rearmost is about three feet tighter than any of them.
Set for the strictest state on the trip. A load that leaves Dallas with the tandems all the way back (Texas has no KPRA rule) is fine until it reaches the Florida line. Before you leave the shipper, list the states you'll cross, find the tightest kingpin number, and confirm a tandem position that satisfies it and keeps both axle groups under 34,000. If no position does both, the load needs rework at the dock.
States not covered here
These twelve were chosen because they carry the most freight and generate the most questions. Other states with kingpin rules worth knowing include New Jersey and Maryland (41 ft to center), Wisconsin (43 ft to center), and several New England states; many western and plains states have no KPRA limit at all. For any state not listed, the safest general setting for a 53-foot van is 41 feet kingpin-to-tandem-center — and the right answer is the state DOT's size and weight page or J.J. Keller's KPRA table. We'll add states as we verify them.
Tools
Sources
- FHWA — Federal Size Regulations for Commercial Motor Vehicles
- J.J. Keller — U.S. kingpin-to-rear-axle allowances (KPRA)
- State statutes and DOT pages are cited on each state page.