When did this style of classic 28' trailer go out of style

Guys, I have a question this is going back to the 1960's through 1980's this is way way way classic GFS.
Back in the day GFS had these tandem axle pup trailers which are pretty much unseen now a days I've seen one once, but I don't know if these were a real production thing or if this was special Michigan order. Do you see it's a tandem axle pup I suppose why not, but any one guess what those are about and was that common equipment among carriers back in the 1960s-1980's. It could have been just GFS, GFS has always had equipment that was uniquely there's makes them pretty cool if you like truck equipment.

Then over the years GFS used this style of converter dolly for many many years they don't really use them anymore although I think up in Michigan there are still a few floating around, what is the advantage using this style of converter dolly over a traditional one? I know that's a pretty western style of converter dolly. I know weight laws in Michigan are a little more then bordering states so most outfits are going to run as heavy as they can.

Anyhow this style of converter dolly does it distribute the weight better? I've heard it's not totally uncommon out west, but for an eastern out fit it's not real common any ideas?
http://www.hankstruckpictures.com/pix/trucks/brian_kuchay/may2003/gfs_trailer.html

http://www.hankstruckpictures.com/pix/trucks/brian_kuchay/2004/feb/gfs_volvo_doubles.html

 

For flat bed it makes sense don't see to many in the refer and dry van world. I know Valley Transport from Ashland, Ohio has the B-Train doubles that are like that.

 

What's weird though is those dollies are not dual but just single rim and tire.

 

That converter dolly style was what GFS used in the 1980's way before the super singles of today. For the most part GFS retired that style of dolly. It's like your regular dolly, but instead of it being a dual it's 2 wheels on both sides you can tell there a little thinner. It's not a piker converter. I guess those converters were really hard to move by hand.