Trucks haul stuff where railroads aren't, among other variables. Another factor which keeps semis viable is the turnaround time for loading and unloading of break-bullk cargo.
If you can fill a container, and there's no particular hurry, trains do the job. If is's pallets of break-bulk, and there's any sort of time factor, semis.
What hasn't hit, yet, as much as it will, is extra consumer costs due to fuel costs. Some, yeah, on the more local level. UPS, for instance, has raised it's fuel add-on, I forget their specific term.
Back to "corridors" for a moment: I've read that semis crossing into the US at Laredo for I-35 north are at some 30,000 per day.
Economic shifts with technology: The Port of Galveston used to make a bunch of income from warehousing cotton for export. With the advent of containers, and the import of stuff from Asia, the railroads gave good prices to ship cotton via container to the west coast. Better that the containers not be sent back empty. So, no more warehousing in Galveston.
I dunno. If you look at the growth in tonnage numbers over the last twenty or so years, you wonder who's buying all that stuff. Obviously, of course, it's all of us. And it's gotta get shipped and folks ain't happy with slow shipments or with traffic congestion and driving hazards.
TANSTAAFL...
Art