It’s done in various places. NJ Riverline is an example. There are a bunch of others.
The bigger problem is the freights just have no interest in sharing the tracks with passenger trains, and requiring heavier and more expensive passenger trains is a convenient way to price the project to death.
The bigger problem is the freights just have no interest in sharing the tracks with passenger trains, and requiring heavier and more expensive passenger trains is a convenient way to price the project to death.