Somewhere here, there's a thread on using the Acelas for high priority mail on the NEC.
And in fact, I've heard of couriers doing just this. For some documents and items, a 1st class ticket on Acela is worth it to get the document to its destination in time.
I think one of the ideas that was hit upon was basically an oversized filing cabinet sized "mail pouch" that could be wheeled on and off. Pound for pound it could make far more than having a passenger there.
That said, right now, if Amtrak wanted to pick up some cargo, they've got the baggage cars. Promote them. I'm still waiting for the day I can get on a train in Albany, with my bike and the same day change trains in NYP to points south. Right now, the only option is to catch the previous day's LSL.
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