Yeah, I think that’s 60 mph average. Level doesn’t matter so much as long as the start and stop points are at the same altitude (due to regeneration).
150ish horsepower is about right. The Tesla Semi has pretty good aerodynamics, though you can only do so much about the trailer part. I’d guess a typical diesel semi is more like 200-250 hp under the same conditions.
The economics are even better.
An average single freight car is probably more than twice the capacity of a semi trailer.
And out west, container trains have two (stacked) 40, 48 or 53 foot containers per car, so a 100 car train of only containers is 200 semi trucks (if fully loaded - you can see in the picture not every car has two) moving between 40-65 mph for hours at a time.
I get stopped by freights all the time on our road. The intermodal one like your picture are as described, but the freight and hopper cars all are around 215-240,000# capacity, so that’s 3.5-4 semis per car.