Unlike out West, where extra long rigs were common or even longer ones could be specially licensed, like that 105′ long 18 unit car carrier a little while back, in the eastern part of the country those were verboten. But there were a few exceptions, on the private turnpikes in New York, Massachusetts, Ohio and Indiana, where double 40′ trailers were allowed. I was so shocked the first time I saw a double 40′ rig in Indiana or Ohio, on the way to NY in 1964. Wow! I couldn’t believe it. What a road train!
From what I can gather, this all started in 1959 on the NY Thruway and Massachusetts Turnpike, and this double load of Larks was apparently on a test/validation run. One of the issues was that they needed to be fast enough to keep up with traffic, which meant the truck companies had to build special high-power tractors. This White is one of them.
The purpose of all this was pretty obvious: to lure truckers from (free) highway 20 and to get them to pay tolls on the turnpikes. Several truck makers offered special high power tractors, and this White cabover 5464TDC, nicknamed the Turnpike Cruiser, sported a Cummins 335 turbo with a 10-speed Fuller Roadranger transmission. 335 hp might not seem like much today, but in 1960, semi trucks typically had some 175-220 hp.
Needless to say, the benefits were obvious, although another tractor had to meet the doubles right after the exit to take on the second trailer. But the practice has spread very widely, and double (and even triple) trailers are allowed in many states.