Originally Posted by k1052
Full grade separation is an FRA requirement for Class 7 track and up, IIRC. Also since there is no electrification in place new locomotives (probably turbine powered) would be needed.
I also seem to recall that some of the curvature on the route inside Michigan isn't conducive to high speed but that could possibly be overcome with tilting trainsets.
Doubt if anyone will switch to turbine powered diesels in the US anymore because of high fuel consumption and high maintenance costs. At current fuel costs, just not going to happen.
To get Acela type speeds, full grade separation will be necessary on the >=125mph portions and really anywhere above 100-110 mph. And the line would have to be electrified, which is going to the less expensive than the curve straightening and grade separation components. Should point out that the NEC still has 11 grade crossings, all in eastern CT on a stretch of the Shore Line East, so one does not have to close all grade crossings to have a 150 to 160 mph train route. Amtrak should restart efforts to close some of those grade crossings permanently over the protests of the NIMBYs, but that is a NEC subject.
The best options in general for electrified HSR corridors in the Midwest will be on abandoned rail lines or barely used lines which can brought from the freight companies and used to construct or cobble together a HSR route. Will not be inexpensive.