Not sure this will work but here goes
Hi! They had a couple like that when building then new tunels here in Stockholm. I read some were that they were easy to turn around in tight spots and load 6-7000kg more than a regular tipptrailer.And you could tipp your load in the tunnel if neaded,regular tipptrailers couldent because the hight when they raise the body.(hope you understand)Havent seen them since the tunnel job was finnished.
Reg Danne
what I can add to Dannes post is that you need the distance from the center of the fifth wheel to the last axle of the trailer to be at least 19m (along those lines, stand to be corrected) to be able to gross 60t, that’s why you need the sliding last axle to remain legal on the road