 The railway tunnel passes under the River Severn from a point just south of New Passage.The engineer Thomas Telford, after surveying the crossing, described it in his report as "one of the most forbidding places at which an important ferry was ever established - a succession of violent cataracts formed in a rocky channel exposed to the rapid rush of a tide which has scarcely an equal".The river between New Passage and Black Rock was 11,200 feet wide at high water and 8,600 feet at low water, in comparison to figures of 6,800 and 4,700 feet for the Old Passage route.