I'd rather pull two 28s than one 53.
............but not 3.
I agree with the double thing, never drove triples though. Another reason some people aren't aware of, the main reason trucking co's use doubles is for scales. Using a single axle tractor and a 53' trailer you could be overweight on the rear tractor axle.
It's called the federal bridge law. Front axle on tractor can be 12K lbs. tamdem rear axles, 34K, tamdem trailer axles, 34K. Adding up to a total of 80K lbs.
A single axle tractor can be 12K front axle, 20K rear, and 34K on trailer axle. Only if you're 34K on the trailer on a 53' trailer you're gonna be over 20K on the tractor axle. I've spoken to some driver's who've gotten ticketed at weigh stations. That's why some places have tamdem drive tractors. (Though what happens is they send the particular load out with a single axle.)
A doubles trailer set up can have 12K on the tractor front axle, and 20K on each successive axle. As long as you under these limits you're OK to go. The load doesn't have to be shifted in the trailer or the axles slid, (they're fixed on pups).
That's why the axles slide on tamdem trailers, to adjust the weight on the tractor and trailer axles for scales. And sometimes a load has to be rearranged in the trailer, (an example is load spacing on a flatbed trailer).
This is why UPS and other trucking co.s uses doubles and pups, it certainly isn't for the 3ft more of freight space. The savings comes from the reduced cost and maintenance of single axle tractors, etc. And there is the ability to split loads going to different places but the same general area.