If that’s what was done, whoever decided to skip the roadbed portion of high speed rail and move straight to the “high speed” part ought to be put away for life. The Shinkansen system in Japan, for example, is a completely separate and specially constructed rail line. And it’s as smooth as riding on air.
It is not “high speed”. It is standard highway speed and therearound. Not even Acela. It is just faster than freight.