Wow, that's pretty slow. The local Amtrak on the Northeast Corridor routinely goes faster than that despite having to stop every 15 miles.
The max speed on the Acela is 150 mph, but the average speed from NYC to BOS is only 66 mph (stops and slow sections) and from NYC to DC only 80 mph. The "150-mph" sections are fairly short. Those are the fastest scheduled times with the fewest stops.
For the Victorville-LV trains, the proposals I've read were always 0 or 1 stop only so it's not as hard to maintain an average near the maximum speed. (The Acela is misleading not because of the stops, but because very little of the trackage is near the top speed.)
Most mainline freight trackage is "Class IV" (max speed 79 passenger, 59 freight) with slower restrictions for curves. The railroads don't have much incentive to go to faster classes as most of the freight they carry isn't that time sensitive that more speed would be worth the higher maintenance costs.
If it's all Class IV and clear, I'm sure they could average 60 mph, perhaps a little higher. There are two caveats though: 1. signaling and 2. track capacity.
1. When I last was paying close attention to US rail (and passenger expansion) 10 years ago they were starting to mandate PTC (positive train control). While I'm not sure exactly what this does I do recall that it prevents trains from operating above the speed limits for any segment of track (including curve and maintenance restrictions) and entering an occupied segment. I think by now the regulators require PTC for passenger trains or a reduction in speed. If there is no PTC it would need to be deployed.
2. Much of the US freight mainline (especially in the west) is single tracked. Only one track shared by trains going both directions with sidings for parking trains to wait. To run efficient passenger operations where the passenger train has some hope of sticking to schedule, which would be needed here, more and longer sidings would likely be needed. In some of the proposals I've read, they replace a parking siding with 5-10 miles of double track so that trains can move in both directions at the same time when they meet.
For a 79 or 110 mph max service the work would involve:
1. stations at each end
2. increasing double tracking and lengthening sidings
3. signaling (if not present)
4. track repair (rails, sleepers, bed, bridges)
and potentially for Class VI speeds (110 mph)
5. tighter sealing of rail corridor to cross traffic (grade separated crossings, fencing, better crossing gates)
From the proposals I've read of this and other corridors many years ago, this could be done for a few hundred million to about a billion dollars including all of these things plus the train sets. (The diesel engines Amtrak uses outside the NE corridor are capable of operating at 110 mph.)
As noted in other posts, this proposal was for much faster service that would have cost much more to deploy. It would have needed a fully sealed corridor (possibly outside the existing freight RR right-of-way) and electrification.
