When a tractor-trailer gets busted up in a traffic accident, where does it go?
I’ve been in several junkyards, and amidst all the junked passenger vehicles (and the odd motorcycle or two) there are no Peterbilts, Macks, etc. Just a few Trailers used for storage.
There aren’t any farm tractors or rockets either but you can buy spare parts for both. You’re in the wrong junkyard. Try a Semi-junkyard
There are wrecking yards for bigger trucks. When I worked in the used parts business, we would occasionally need parts for our hulk haulers, would would get the parts from a truck wrecking yard. Another thing to consider, there are millions of vehicles on the road in the US, tractor trailer rigs make up a very small percentage of these. Cars don’t last as long as trucks either. Many trucking companies also keep there wrecked trucks for spare parts. Find a place where a trucking companies parks their trucks and you will find some wrecked trucks along the back fence.
. . . and I’m sure you will find that truck operators are much more inclined to make repairs and replace parts from wrecked vehicles than the dealers in passenger cars.
A passenger car that has been wrecked or has been restored from salvage parts is very obvious to anyone competent enough to run a used car lot and thus the value is significantly decreased. A long haul truck with some replacement parts is running on a purely utilitarian basis and nobody cares that the parts may have been salvaged. The thing just has to turn miles.
For the same reason why you don’t stumble on dead elephants or other large game out in the open. Like other big game, semis manage to crawl their way to that special secret place to die when its time 
As an aside, when an insurance company pays a claim on one of these trucks, the cargo must be destroyed. I’ve heard stories from guys who work for the state highway department of millions of dollars worth of TVs having a hole dug for them, and being buried right next to the interstate. Chocolate, wine, you name it, simply destroyed. 
That’s BS.
The insurance company would take possession of the material and then auction it off or try to claim the value back.
I highly doubt that there is a place in this country where have they dug holes for new TVs or cases of wine just to bury them.
I’ll ask him if he was pulling my leg next time I see him, but I specifically remember him telling me about driving a loader and pushing cases of wine and chocolate into a hole with a loader. Most of the merchandise isn’t going to survive, and it might cost as much to sort what can be sold as one would get from the selling. For example, the local brewery gives beer to their employees if a single bottle breaks in a case; it’s less expensive form them to write it off than it is to have somebody clean and relabel each bottle.
sounds like an urban legend to me. “Buried right next to the interstate”? Huh?
On whose property? Under which zoning authority?
I ain’t no lawyer, but I’m pretty sure you can’t just drive a backhoe onto somebody else’s property, rip up the landscape and dig holes wherever you get the urge, just because you feel like burying something…
(come to think of it…that might make a good plot for a mystery novel…)