California Trailer Length and KPRA Rules: STAA vs California Legal Trucks

The direct answer: on the Interstates and other routes open to STAA trucks, California allows a tractor with a semitrailer up to 53 feet, with no overall length limit, as long as the kingpin-to-rearmost-axle distance (KPRA) is no more than 40 feet on a trailer with two or more axles, or 38 feet on a single-axle trailer (Vehicle Code 35401.5). Off those routes, a “California Legal” tractor-semitrailer is limited to 65 feet overall with the same KPRA limits. Sliding the tandem changes the KPRA, so it is worth checking every time.

Two kinds of tractor-semitrailer

Caltrans sorts tractor-semitrailers into two categories: STAA trucks (shown green on its maps), named after the 1982 federal Surface Transportation Assistance Act, and California Legal trucks (shown black). Which one you are depends on the combination’s dimensions, and it decides which roads you may use.

Single trailer

• STAA: overall length unlimited; semitrailer up to 53 feet; KPRA up to 40 feet (two or more axles) or 38 feet (single axle). A semitrailer up to 48 feet meets the length condition without the KPRA test (Vehicle Code 35401.5(a)(1)).
• California Legal: 65 feet overall (Vehicle Code 35401(a)); semitrailer length not separately limited; KPRA up to 40 feet (two or more axles) or 38 feet (single axle).

Doubles

• STAA: overall length unlimited; neither trailer over 28 feet 6 inches (Vehicle Code 35401.5(a)(2)).
• California Legal: either 75 feet overall with both trailers no longer than 28 feet 6 inches (Vehicle Code 35401(b)), or 65 feet overall with one trailer limited to 28 feet 6 inches.

Which roads: the route colors

The official source is the Caltrans California Truck Network map, also in QuickMap under the commercial vehicle options. Caltrans says private atlases and GPS truck routing cannot be guaranteed and must be checked against it.

• Green — mainly Interstates. STAA and California Legal trucks.
• Blue — signed state routes open to both.
• Black — state routes for California Legal trucks only; no STAA trucks.
• Yellow — KPRA advisory routes, California Legal only. Caltrans advises against using one unless your KPRA is no more than the posted figure, which is 30 feet on most of them.
• Red — a specific restriction; read it on the map to see whether it applies to your truck.

Leaving the network for fuel, food, lodging or repair

An STAA truck may leave the network to reach fuel, food, lodging and repair facilities within one road mile of an identified exit, where that access is consistent with safe operation (Vehicle Code 35401.5(c)). Caltrans marks these exits with a blue Service Access “S” sign, and Terminal Access routes with a “T”. Before heading to any shop off the network, ours included, check the route on the map rather than trusting the GPS.

KPRA, measured and changed

KPRA is measured from the center of the kingpin to the center of the rearmost axle. On a trailer with a sliding tandem, every slider position is a different KPRA: slide the tandem back for weight distribution and a 53-foot trailer can be over 40 feet. Know where your legal slider positions are, and make sure the slider locking pins are fully engaged after every move.

Slider pins that will not seat or release, worn pin holes, a damaged slider rail or a release handle that will not hold are trailer repairs, not something to work around at a scale house. See trailer repair, and the annual DOT inspection guide for what an inspector looks at on the trailer.

Common questions

Can I run a 53-foot trailer in California?

Yes, on routes open to STAA trucks, if the KPRA is no more than 40 feet on a trailer with two or more axles (38 feet with a single axle). As a California Legal truck the 65-foot overall limit also applies.

What does KPRA mean?

Kingpin to rearmost axle: the distance from the center of the trailer’s kingpin to the center of its rearmost axle. California limits it to 40 feet on trailers with two or more axles and 38 feet on single-axle trailers.

Can an STAA truck drive to a repair shop off the Interstate?

Vehicle Code 35401.5(c) allows access to fuel, food, lodging and repair within one road mile of an identified exit, where that access is safe. Check the Caltrans truck network map and posted signs for the route.

Are GPS truck routes reliable for this?

Caltrans says private route guides and GPS cannot be guaranteed and must be checked against the official California Truck Network map.

Summarized from California Vehicle Code sections 35400, 35401 and 35401.5 and the Caltrans Quick Guide: Truck Lengths & Routes, reviewed 2026-10-20. Plain-language summary, not legal advice; the code, posted signs and enforcement officers govern.