One demonstrated issue with Iron Highway is that it requires kingpin-hitch securement at the trailer noses. At least one of these has come unlocked in the all-too-familiar-with-wear-on-the-equipment way and caused the usual problems. The aftermath of such an event may eat up a great deal of the presumable profit from using Iron Highway instead of, say, expanded conventional containerized intermodal in lieu of van trailers. In my opinion there is also the added question of the skills needed by drivers for circus-type loading and unloading when there is a considerable narrow distance to back up between presumably substantial sill rails. This is not a 'kangarou' system with bearing surface between the trailer duals, so presumably scuffing the trailer outer sidewalls is the 'default' guidance backup. With the current 'driver shortage' are there enough skilled or trainable drivers to make an expansion of Expressway safe and practical?
The kingpin hitch has been in use for 60 years or so. It holds on in train wrecks, TOFC cars sent over humps, and overspeed impacts. If all rail components were nearly as reliable as a hitch there would be far fewer problems. Failure of a flatcar trailer hitch is the last thing we need to worry about.
As far as finding workers capable of backing trailers onto flatcars, don't underestimate the abilities of the average worker. With proper equipment, some training, and respect they can do great things. And they'll take great pride in their work. If they're allowed to.
The truck driver "shortage" is caused by: 1) not paying enough and, 2) miserable working conditions that can cause a driver to be away from home for weeks on end while living in his/her truck. Pay more and get the driver home and there will be enough drivers.
My girlfriend's son is a driver in Chicago. He doesn't mind starting early and working late six days per week. But he has a 15 month old son at home with his wife. He wants to bring in a good paycheck to care for them and be with them at night. He won't go out over the road (driver shortage?) but he'll work his tail off for his paycheck and his family time.
Don't ever underestimate the workers' abilities. They can do a whole lot of good things, under the right conditions.