I think the answer is somewhat. The problem is that you have bottlenecks in various parts of the system. The other major problem with using those existing corridors is grade crossings. There are literally thousands of grade crossings on those main-line corridors. You absolutely cannot have grade crossings with high-speed rail. It would be a public safety disaster.
It may not be feasible from a cost point of view to look at those corridors. You may have to look at other corridors where you do not have that issue, at least not to the same degree.