What is the rationale for the Bridge Laws?

King Pin to Rear Axle was a bone the feds threw the states when they allowed 53' trailers on Surface Transportation Assistance Act, STAA roads. One of the things STAA did was standardize weights and lengths on STAA roads. Those are interstates, US Highways and most state numbered highways. Before STAA, states east of the Missouri River limited length to 55'. That's why cabovers were king. STAA standardized length to 48' trailers, 102" wide and 80,000 on five axles, assuming it meets bridge law. This took control away from the states. A little was given back with the KPRA law. States were free to implement it. It is about control. In California there is no KPRA law for 48' trailers, only 53'. Now a 48' with the axles back is legal, and KPRA would be longer than is allowed on 53' trailer.

As far as the nomenclature, drivers use the wrong term all the time. "Safe haven" when they mean "safe parking". That's another pet peeve of mine.

 

Why, when I have a stretch trailer at 75 ft I can haul less weight than when the trailer is at 45 ft?

California has decided that 80,000 lbs is ok at 40 ft kpra. Some other places are different.

Bridge law has to do with the terrain you are on, including bridges over water, but not exclusively bridges.
Why are there spring thaw laws? It's not because of the bridges,

It's all ''engineered''.

 

This may help in understanding bridge laws:

This spreadsheet is available at the url listed in the blue box for anyone who wants to play with it.

In Idaho, one can purchase an excess weight permit for divisible loads. The maximum weight used to be 105,500, but the beet haulers and other bulk commodity haulers managed to lobby for weights up to 129,000, BUT, you have to be legal based on the bridge formula, and I think it is route specific as well. I use this for our 48' spread axle flatbed to know what I can legally haul on our excess weight permit. The example below was for a three-axle side dump trailer that I rented. I have bumped up the weights so that the bridge on 2 through 6 is over, just for example. As you can see, despite having an excess weight permit for 129,000, I can only gross 91,000 with this configuration.

@Long FLD described this, but I thought it could be useful for further understanding.

 

I always get a kick out of that too..
My 48' fixed spread is 44'3" KPRA, yet legal everywhere & don't corner worth a darn.. lol

Personally feel lots of these "laws" on the books are just a money grab..

 

53’s weren’t, maybe still aren’t I no longer have an OR permit with the maps, allowed on 138 going east out of Roseburg OR. But my friend could load 60ft beams on his 48ft spread and be perfectly legal.

 

Wrong again.

It’s 89.5 FM out in Ukiah, California.



It’s tough being the smartest guy in the room sometimes.

 

King Pin to Rear Axle

 

I thought that was a Cincinnati station?

 

WKRP

And thanks. Now I'll be singing it for the rest of the day.

 

At your service! Lol