Return of the Vista Dome Car?

As I remember reading… the long ago former restriction they could not run Budd Full view, Vista Domes (the latter CZ type) on some routes without having a smaller clearence Vista Dome…in fact, I think it was the C&O or B&O that had that restriction. They had those retarded looking sloped dome cars. Not sure if that restriction is still in place. However that is what I was referring to.