The operational constraints of US freight trains would probably limit passenger train speeds to sub-100mph on mixed lines, but even if they could run at 90mph and maintain a reliable schedule with such route upgrades, it would be workable. When passenger trains were privately run, they were able to move both efficiently because many rail lines were double tracked decades ago. You'd have to be comfortable with paying private railroads enormous amounts of money to double track and upgrade some of their PSR-shitofied mainlines (not saying that's wrong, just how such a deal would have to go). It wouldn't be as expensive as building a new segregated passenger line in most cases, but it wouldn't be easy, quick, or cheap either.>>1649674>In fact I'd even go so far as to say that the possibility of high-speed freight makes that preferable to segregating the rails.
Unfortunately speed doesn't sell in freight rail these days. Maybe in the future some expedited freight service will be economical. There would need to be major changes in philosophy and infrastructure to do it.>But something must be done to speed up the trains.