The current tunnel is a relic from a long time ago when trains were slower, and there were competing train lines that had to try and fit through baltimore where they could. If you look at a map of the train line, it actually sharply curves out of the way of that currently Black neighborhood to go under the currently white neighborhood. This means the top speed is 30 mph. Under the new plan, they could hit 100 mph.
There are other problems with the current tunnel, mainly just down to being old, and those you could fix by redoing it in the same spot, but that wouldn’t fix the speed issue, because the speed is governed by the curvature (and grade).