The Act was passed on 7 August 1896 for the line, seven miles in length, but the running powers were refused. Descending from Penrhos Junction, the existing Rhymney Railway line to Walnut Tree Junction dropped down into the valley by a long and steep gradient at 1 in 48 but the Barry Railway's new line, parallel in this area, remained at a higher level and crossed the railways, river and canal in the Nantgarw gap by the Walnut Tree viaduct of 517 yards.