I have emailed Kato regarding them releasing the Volvo tractors, in a manner as did Atlas, in two packs or something of the like. In their reply, the only thing they said was "the price point we have is for both tractor and trailer. Thank you for contacting us here at Kato USA", along those lines. It kinda pissed me off as they didn't answer my question/request very well, and only thing I got from it was, tough luck, buy the set and sell the trailer.
Also, Atlas just released in O Scale a model of a Freightliner with sleeper, seen it on their Facebook page a little while back. I told them they need to release that tractor in N Scale, to go along with all their Pines Trailer releases.