Caiff y gwaith ategol hwn, a gomisiynwyd gan Lywodraeth Cymru, ei gynnig yn dilyn cyhoeddi'r Achos Dros Fuddsoddi gan yr Athro Mark Barry. Nododd weledigaeth ac amcanion ar gyfer gwella Prif Reilffordd y Gogledd a rheilffordd Wrecsam-Glannau Mersi ar ôl trafod yn helaeth gyda rhanddeiliaid.
The supplementary work which has been commissioned by the Welsh Government follows the publication of The Case for Investment by Professor Mark Barry which identified a vision and objectives for improvements to the North Wales Main Line and the Wrexham-Merseyside line following extensive engagement with stakeholders.