40 Feet from Kingpin

On our way over the Hillsborough Bridge on Boxing Day, I took this photo of the side of a semi-trailer parked on the trail construction site.

Photo of the sign on the side of a truck.

Following up later in the day, I fell down a fascinating rabbit hole, learning about the “king pin to rear axle distance,” and why this is important.

The “king pin” is the place where the trailer attaches to the truck pulling it. The 40 foot distance is important (and thus labelled) because in California there’s a regulation, known colloquially as the “Bridge Law,” that on a typical 53 foot trailer, the maximum distance from the king pin to the rear axle is 40 feet, and the weight over the axles cannot be more than 34,000 pounds.

The 40 foot distance varies from jurisdiction to jurisdiction; California’s in the shortest limit, and thus a kind of effective baseline.


Oliver (fs)'s picture
Oliver (fs) on December 31, 2020 - 13:14 Permalink

So is that trailer too long to drive into California? I can’t tell if it’s fore or aft of the rear axle

Peter Rukavina's picture
Peter Rukavina on December 31, 2020 - 14:08 Permalink

The reason for the label is to guide drivers as to the maximum distance they can slide the rear wheels back (the wheels at the back, I have learned, are adjustable). So “it depends” is the answer, I think.