Why is it 40’ kingpin length in Ca?

Yes they are.

 

Did you happen be out by Isleton when that happened? Sounds about right for that area, go right end up in the river, go left end up in the slough.

 

I pull some 48’ steps with the 24” kin pin setting and the the rear axle/axles(spread and close tandems) all the way to the rear, talking about getting around certain areas……. This is were your professionalism and judgment radius comes to play.

 

What is really needed is remedial education on tail swing….more stuff tore up in warehouses and pkg lots that way

 

It's because it's the ###hole of the universe.

 

Sorry for the long ai response, I’m lazy today.

The California law in question is outlined in Vehicle Code § 35401(b)(4), which limits the kingpin-to-rear-axle (KPRA) distance on a semitrailer (when coupled to a truck tractor) to a maximum of 40 feet if the trailer has two or more axles, or 38 feet if it has a single axle. (Cities and counties can further restrict this to 38 feet on roads under their jurisdiction per § 35401(e), and the California Department of Transportation can recommend restrictions with advisory signage on certain highways per § 35401(f).) This applies particularly to longer trailers; there is no KPRA limit for semitrailers 48 feet or shorter in length, but the restriction kicks in for those exceeding 48 feet (such as common 53-foot trailers) to comply with federal mandates while addressing state-specific concerns. Exceptions exist via permits for specialized uses, like motorsports trailers up to 46 feet KPRA per § 35401(g)(1) or agricultural equipment up to 48 feet.

The primary reason for this limit is to promote vehicle stability and public safety during turns, especially on California's diverse roadways that include urban intersections, mountainous curves, and tight rural routes. A longer KPRA increases the risk of "tail swing" (where the rear of the trailer swings outward during sharp maneuvers, potentially striking adjacent vehicles, pedestrians, or infrastructure). This can lead to accidents, as highlighted in enforcement reports and incidents like a 2022 Bay Area bridge collapse attributed in part to improper heavy-haul configurations. The restriction also aids in even weight distribution across axles, reducing excessive wear on roads and bridges by aligning with California's bridge formula laws (which cap trailer axle weights at 34,000 pounds when at or near the 40-foot mark). Overall, it's designed to balance commercial trucking efficiency with protecting infrastructure and minimizing collision risks in a state with high traffic density and varied terrain.

Historically, the 40-foot KPRA limit emerged as California's adaptation to the federal Surface Transportation Assistance Act (STAA) of 1982, which required states to permit longer trailers—at least 48 feet (and later commonly 53 feet)—on designated "national network" highways without imposing overall length limits on tractor-trailer combinations. Prior to STAA, trailers were typically limited to 45 feet or less nationwide, and California had stricter vehicle length rules dating back to the original 1935 Vehicle Code (which consolidated earlier traffic statutes). To comply with the federal law while preserving safety on its roads, California amended its Vehicle Code in the early 1980s to allow the longer trailers but introduced the KPRA cap to control off-tracking and swing issues in configurations that would otherwise be too unwieldy. Key milestones include the 1982 STAA enactment, subsequent state amendments to §§ 35400–35401 around 1983–1984 to align with it, and a 1988 legislative requirement (effective January 1, 1989) for Caltrans to post advisory signs on highways unable to safely handle maximum KPRA vehicles. The limit has remained largely unchanged since, with ongoing enforcement by the California Highway Patrol and occasional permits for industry-specific needs, reflecting a compromise between federal deregulation of truck sizes and state-level safety priorities.

 

I got into some interesting places the years I was hauling cattle out there, 280” wheelbase and a 52ft spread. Lol. Somewhere I have an old phone with a pic of my truck coming out on a road with a sign posted vehicles over 35ft not advised.

 

If it were all about 53's on certain non-interstate roads, then they should simply put a bridge length limit on specific roads. Think like a politician...'how much fine revenue will we lose if we change the law'. Bottom line, it's all about the Benjamins at this point.

 

It has nothing to do with weight, so it has nothing to do with bridge. It’s not any different than any other state that has various restrictions on trailers over 48ft. Florida has a KPRA regulation but will sell a permit if you have fixed axles. Idaho requires a permit for trailers over 48ft if you’re off the national network.

When I got caught with a 52ft spread the fine was $137.

 

Thats exactly it ! Isleton bridge.. one side of the bridge is nice and wide easy turn. Other side is big enough for like a box truck. I was on that side... I attempted the turn even after swinging wide out off the road as far as i could. Didnt make it halfway . Bad part is i knew i wasnt gonna make it and still tried it... Then i had to backup with traffic behind me.. lol going down the road further wasnt exactly graat either... A 8ft wide lane turned into like 6ft wide and then i started trimming tree branches, thats when u know ur really ####ed and completely off a truck road.. luckily there was a boat launch a good distance down the road that was big enough to back up into. Funny enough i could see dual tire tracks there when backing up so atleast i wasnt the first dummy to do something like that .