Here in AZ, total length is 75' and first coupler MUST be a fifth wheel. Second coupler can be another fifth wheel, pintle or ball hitch. Can NOT have a ball or pintle as the first hitch.
Saying this, there used to be farmer down Yuma way that would hook 4 loaded cotton trailers together, about 8,000 lbs EACH, with clevis hitches and tow the whole train down I-8 from his farm to the cotton gin. He'd pull EIGHT empties back...usually running 70-75 mph, according to my dad. Zero brakes on anything but the truck. :-)
Lyle