What is the rationale for the Bridge Laws?

I used to work for a trucking company that had a diagram showing two different trucks on bridges to show how tandem placement can affect the weight distribution on bridges. The diagram looked something like the drawing in the photograph below:



Now I totally understand why a short 80,000 pound tractor-trailer would strain a bridge more than a long 80,000 pound tractor-trailer like in the drawing in the photograph above. In other words, I understand why if there are two tractor-trailers of the same weight, the tractor-trailer with the shorter wheelbase will strain the bridge more than the tractor-trailer with the longer wheelbase.

Here's the part that totally baffles me: Why do the bridge laws force drivers to keep a shorter wheelbase?

Since the tractor-trailer with the longer wheelbase strains a bridge more than a tractor-trailer with a shorter wheelbase if the two tractor-trailers are of equal total weight, I would have expected the bridge laws to force truckers to slide the tandems to the rear. I would have expected the purpose of the bridge laws to prevent truckers from having too short a wheelbase. Instead, the bridge laws prevent truckers from having too long of a wheelbase.

California has the strictest bridge law of all, requiring the distance from the kingpin to a point on the rear axle to be 40 feet OR LESS.

Since a shorter wheelbase puts more of a strain on a bridge than a longer wheelbase for a given weight, why is the purpose of the bridge laws to prevent the wheelbase from being too long (instead of too short)?

 

Well, I suppose they don't DIRECTLY force anyone to have a shorter distance between their drives and their tandems. The bridge law force trucks to have a shorter distance between the kingpin and a point on the REAR AXLE ASSEMBLY. So, in practice, it does force people to have a shorter distance between their drives and their tandems.

"We've got to slide the tandems forward. We're going to California."

I've worked in the industry for over 8 years, starting in 2012. I've drove for three trucking companies. EVERYONE at every trucking company I ever worked for and everyone at the truck driving school I attended referred to the laws dictating the maximum distance between the kingpin and the rear axle assembly as bridge laws.

 

Do you mean that when people call the laws that dictate a maximum distance between the king pin and the rear axle assembly a bridge laws, the word "bridge" refers to a part of the tractor-trailer?