Texas Bridge Law: Axle Limits and the Bridge Formula

Texas writes the federal bridge formula directly into state law and applies it on every highway, with the standard 20,000 / 34,000 / 80,000 limits. What Texas does not have is a kingpin-to-rear-axle rule for a 53-foot van — the state allows semitrailers up to 59 feet with no KPRA cap.

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

The numbers at a glance

Limit	TX	Where it comes from
Gross weight	80,000 lb	Transp. Code 621.101, "including all enforcement tolerances"
Single axle	20,000 lb	621.101
Tandem axle	34,000 lb	621.101; 36-ft rule for two consecutive tandems
KPRA / wheelbase	No statutory KPRA limit for a 53-ft trailer	Semitrailer max 59 ft (621.204); no kingpin-to-rear-axle rule found
Bridge formula applies?	Yes — statewide	W = 500(LN/(N−1) + 12N + 36) is in 621.101

Legal limits change and enforcement varies by road. Confirm anything you're betting a ticket on with TxDMV / Texas DPS.

How Texas applies the bridge law

Texas is about as straightforward as bridge law gets. Transportation Code 621.101 spells out the federal formula — W = 500(LN/(N−1) + 12N + 36) — and the three headline numbers every driver knows: 20,000 on a single axle, 34,000 on a tandem, 80,000 on any group of consecutive axles, each "including all enforcement tolerances," which is the statute's way of saying there is no built-in cushion. The same section carries the 36-foot rule: two consecutive tandems may each carry 34,000 lb if the first and last axles of the two sets are at least 36 feet apart.

Trailer geometry is where Texas is generous. A semitrailer in a tractor-semitrailer combination may be up to 59 feet long (621.204), and neither the Transportation Code nor TxDMV's size and weight page sets a kingpin-to-rear-axle distance for it. For a 53-foot van that means you can put the tandems wherever the weight needs them — as long as the axle groups and the 36-foot span still clear the formula.

The practical Texas trap is the opposite of California's: drivers slide the tandems all the way back for a heavy nose load, get comfortable, and then cross into a KPRA state on the same setting. Texas won't write you for it; the next state will.

How to slide your tandems for Texas

With no KPRA cap, Texas is where the slide calculator alone answers the question. Scale, find the heavy group, move the tandems toward it until both groups clear 34,000, and check that your drives-to-trailer-axle span is still 36 feet or more if both tandems are near the limit.

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 Texas 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 Texas

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 — the ordinary overweight-axle citation; Texas DPS Commercial Vehicle Enforcement works fixed and portable scales statewide.
Gross over 80,000 without an overweight permit. Texas fines scale with pounds over the limit; verify the current schedule with Texas DPS.
Bridge-formula violation on a short inner span when tandems are slid far forward and the four-axle drive-plus-trailer group drops under 36 feet. Less common on vans, more common on spread-axle and specialty trailers.

Texas bridge law FAQ

Does Texas have a kingpin-to-rear-axle law for 53-foot trailers?

No statutory KPRA limit was found for Texas. The state allows semitrailers up to 59 feet (Transp. Code 621.204) without a kingpin rule. If your route continues into a KPRA state, set the tandems for that state before you leave.

Does Texas apply the federal bridge formula on state highways, not just Interstates?

Yes. Section 621.101 applies the formula to a "group of two or more consecutive axles" on the highways of the state generally, not only the Interstate.

What is the "2.5% per foot under 12 feet" rule on the TxDMV page?

It appears in TxDMV's permitted-weight rules: when consecutive axle groups are spaced less than 12 feet apart, the permitted weight is reduced 2.5% per foot under 12. It concerns permit loads, not legal 80,000-lb operation.

Does Texas allow any tolerance on axle weights?

The statute says the limits apply "including all enforcement tolerances," so plan on the raw number. Do not assume a cushion.

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.