I would like to scratchbuild an adaptation of the European rolling-highway (Rollende Landstrasse or RoLa) trains used to ferry tractor-trailers and their drivers:
Of course these are not available in 'O'. They do exist in HO scale, and I have on more than one occasion thought about acquiring a set of the HO cars in order to clone them in O from sheet styrene. The biggest problem however is the oddball four-axle trucks these extra-low flatcars ride on:
Making the sideframes would be a challenge, but the wheelsets could be a show-stopper...the best information I can get my hands on suggests they max out at about 13"-15" in diameter. Anyone know how to make (slightly more than) quarter-inch diameter wheelsets for 3-rail track? I suspect a lathe may be necessary, but I don't have access to or anyplace to put one, much less operate it.
But if those issues could be overcome, getting tractor-trailers to put in them would be the easy part.
Well if you visually disect that truck, it appears to be a superliner truck with an extended bolster to accommodate the steel rotating joint.