Ah, so you meant to differentiate between container-carrying and standard enclosed semi-trailers? However, that's not a core difference between RoadRailer and RailRunner's Terminal Anywhere technology (particularly if I interpet RailRunner's note about "a trailer solution can also be made available" right), and I don't think there can be that much difference in freight capacity.

IMHO the limiting factors in a US context are not AAR- but road-related: the 13.5' outer height limit and the standardised 47-49" fifth wheel height. So the front end external height of the cargo-holding structure cannot be larger than 115". A high-cube container is 114". So what about the inside? Checking figures, high-cube container internal height is 106", while Triple Crown dry vans have an inside height of 110" at the front and 112.25" in the rear. So in effect the 4" thick bottom of the container (about 10 cm) and a slope 2.25" high at the end is what's gained.

If RailRunner (or any new RoadRailer version) comes to Europe, they'll need to lower their stuff by about 10 cm to fit roads, but fortunately that won't reduce the cargo height: both the road vehicle height limit (4 m or about 13'2") and the standard fifth wheel heights (seem to be between 950 and 1,150 mm, or about 37" and 45") are lower.

if there is a more "rounded" loading gauge in the target network, the top of the Roadrailer trailer could be made higher

If a trailer is designed to fit the rounded corners of older railway loading gauges in Europe, then it will have a smaller capacity than a standard road trailer while already being more expensive as a special rail-ready construction, and thus be at a disadvantage.

_{*Lunatic*, n.
One whose delusions are out of fashion.}