Shildon Tunnel

Shildon Tunnel is a railway tunnel on the Tees Valley line between Shildon, and Bishop Auckland in County Durham, England. Although designed to have two tracks, the line is single-track through the tunnel and on to Bishop Auckland. It was opened out in 1842 by the Shildon Tunnel Company to avoid a railway incline over the 100-foot (30 m) hill that the tunnel bores through, and later sold outright to the Stockton and Darlington Railway (S&DR). By at least 1880 rolling stock was wider and the tunnel could not accommodate two trains passing through at the same time; the two tracks were reduced to a single track in 1967 after many years of single-train occupancy.

Tunnel data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).