They are routine on American freight lines, where there are a lot of single track lines and political issues between the freight companies and passenger trains.

They are routine on American freight lines, where there are a lot of single track lines and political issues between the freight companies and passenger trains. https://openrailwaymap.org/ https://openrailwaymap.org/ shows (if you zoom in far enough) that at least some lines around Atlanta are only single track. https://www.trains.com/wp-content/uploads/2020/10/multi-track-main-lines-map.pdf https://www.trains.com/wp-content/uploads/2020/10/multi-trac... suggests most of them are. It isn't a common issue in Russia or China (similar rail freight use to the USA). Double tracks means no waiting for opposing trains, and it's then straightforward to fit passenger trains, which stop at stations but go faster, between constant speed freight trains. It does mean twice as much track must be maintained to a higher standard than freight-only track.