The conveyor belt thing has a lot of momentum behind it. There's a push to created automated logistical grid that replaces TEUs with a smaller more manageable and routable standard. Self driving and traditional rail just have extraneous overhead that a basic conveyor with switching simplifies.
Well belt conveyor definitely isn't the right approach - it's about 1.5-2x more expensive than other types of pallet conveyor (e.g. chain) and is difficult to maintain (snapped belts etc). Line shaft is another option, but has similar drawbacks to chain at this scale.
Also bear in mind that pallet conveyor is slow - in most factories or warehouses where you are covering large distances the standard approach would actually be to put a rail guided vehicle in (often called a pallet monorail).
Plus conveyors would then need to be enclosed (they have lots of moving parts - it's not like train rails where you can just put them outside and let it get wet. The pallets also can't get wet, but it would take less infrastructure to cover the pallets than cover the full 310 mile route.).
A material ropeway would be another option - not commonly deployed but probably a much better fit for moving pallets across these sort of distances and much faster than conveyor (although still probably only 15-20 miles per hour!).
