[Coroner]

The biggest reason the trucks are going to continue to run cross country simply has to due with IFTA. The fuel taxes that truck owners pay for as calculated by how much carbon fuel emmissions they burn in each Jurisdiction (State) based on MPG.
It's how the NAFTA deal was sold.

Freetrade my **s! Grab the taxes is more like it!
It is the reason trucks will still haul the ridiculous miles they haul. I used to drive the big rigs, now I drive a much smaller vehicle and provide a more focused service. You won't get a big rig where I usually go, nor a box truck for that fact.

But, too stay on topic as a reply to Big Dave. IFTA is the unseen culprit.