Indiana Bridge Law: Axle Limits and the 43-Foot Kingpin Rule

Indiana adopted the federal bridge formula as state law in 1975 and runs the standard 20,000 / 34,000 / 80,000 limits under IC 9-20-4-1. Its kingpin rule is 43 feet from the kingpin to the rearmost axle for semitrailers over 48½ feet on the state highway system — measured to the rear axle, not the tandem center.

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

The numbers at a glance

Limit	IN	Where it comes from
Gross weight	80,000 lb	IC 9-20-4-1
Single axle	20,000 lb	IC 9-20-4-1
Tandem axle	34,000 lb (no axle over 20,000)	IC 9-20-4-1; 36-ft rule for two tandems
KPRA / wheelbase	43 ft, kingpin to rearmost axle	IC 9-20-13-4; semitrailers over 48 ft 6 in on the state highway system; 46 ft motorsports
Bridge formula applies?	Yes — statewide	Adopted as state law; ISP size & weight summary

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

How Indiana applies the bridge law

Indiana Code 9-20-4-1 sets an overall gross limit of 80,000 lb, 20,000 lb on a single axle, and 34,000 lb on a tandem group with no individual axle in the group over 20,000. The 36-foot rule is written in: two consecutive tandems may carry 34,000 each provided the distance from the first axle of the first set to the last axle of the second is 36 feet or more. The federal bridge formula governs any other group of axles, and because Indiana adopted it as state law, it applies on state routes as well as the Interstate.

The kingpin rule is IC 9-20-13-4. A semitrailer longer than 48 feet 6 inches may operate on the state highway system if the distance from the kingpin to the rearmost axle is not more than 43 feet (46 feet for trailers used primarily for motorsports). Indiana measures to the rearmost axle rather than the center of the tandem, so compare it to California's 40-foot rearmost-axle rule, not to the 41-foot-to-center rules in Pennsylvania and Tennessee. In practice, 43 feet to the rear axle is roughly 41 feet to the center of a standard tandem — about the same as the eastern norm. IC 9-20-13-2 caps the semitrailer itself at 53 feet.

Indiana State Police's Commercial Vehicle Enforcement Division runs fixed scales on I-65, I-70, I-74, I-80/94, and the Toll Road, and the state's summary of Title 9 size and weight laws is a useful one-stop reference for the current figures.

How to slide your tandems for Indiana

Set the tandems so the kingpin-to-rearmost-axle distance is 43 feet or less, then slide for weight. Indiana's rule and Illinois's 45'6"-to-center rule are both comfortable on a 53-foot van; Michigan's wheelbase band to the north is tighter, so set for Michigan if you are heading up I-69 or I-94.

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 Indiana 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 Indiana

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 and gross over 80,000 — Indiana fines are per-pound over; ISP publishes the schedule.
KPRA over 43 feet on a 53-foot trailer on the state highway system, usually paired with an overlength charge.
Toll Road weight violations — the Indiana Toll Road has its own enforcement and posted limits; verify with the operator.

Indiana bridge law FAQ

What is Indiana's kingpin-to-rear-axle limit?

43 feet from the kingpin to the rearmost axle of the semitrailer, for semitrailers longer than 48 feet 6 inches operating on the state highway system (IC 9-20-13-4). Motorsports trailers get 46 feet.

Is Indiana's kingpin rule measured to the rear axle or the tandem center?

To the rearmost axle. That makes 43 feet in Indiana roughly equivalent to 41 feet measured to the center of a standard tandem.

Does the bridge formula apply on Indiana state routes?

Yes. Indiana adopted the federal formula as state law, and IC 9-20-4-1 applies the limits to Indiana highways generally, not only the Interstate.

What is the 36-foot rule in Indiana?

Two consecutive sets of tandem axles may each carry 34,000 lb only if the overall distance between the first and last axles of the two sets is 36 feet or more.

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.