matchmaker
Established Member
There are a lot of single lines around the country that were built with earthworks and structures to support a double line, which never took place. Over time the track may have been centred in places but the original wide structures are still there. The Bluebell north from Sheffield Park is an example.
Nocks book on the Highland Railway mentions that all the bridges and viaducts on the Direct Line via Carr Bridge were built to accomodate double track.