I hold a Class A CDL in Texas and have double/triples endorsement. I was a bit fuzzy on the definitions so I went back to the TX CDL manual. A double is a combination of 2 trailers pulled by a tractor and a triple is in fact a combination of 3 trailers pulled by a single power unit. I haven't looked at the other states CDL manuals, but the CDL is a national license per se, so I think the definitions are the same across the board. So a pickup pulling a fifth wheel pulling a utility trailer by this definition is a double. There are in fact very few states that even allow pulling commercial triples, I know TX does not, but you don't see TX in the RV/Boating lists that don't allow triple towing. Most states do allow commercial doubles.