the second by 21 adits which passed underneath Nicholson's tunnel, allowing spoil to be removed by boat. Construction was disrupted by strike action by tunnellers and bricklayers over disputes about payment and shift length. In February 1871, the second rail tunnel, south of the first, was opened. Even two tunnels could not provide sufficient capacity to satisfy demand and in 1890, the L&NWR embarked on providing four tracks on most of the line which required constructing a new twin-track tunnel. Construction was done under the guidance of A. A. MacGregor and carried out by 1,800 men who lived in the paper mills at Diggle and 54 wooden huts near the eastern side. Once again the tunnel was driven from adits, this time 13 adits were connected to the first railway tunnel. The canal tunnel was extended at the Diggle end to accommodate the third rail tunnel, which ran close past it. For most of its length, the new bore is to the north of the canal tunnel, but passes over the canal tunnel just inside each tunnel entrance. When the work was completed, the tunnel was long. To speed the excavation, 40 breakups were opened using around of gelignite. About 25 million bricks, mostly produced locally, were used in the tunnel lining. A unlined section of tunnel collapsed in April 1894 blocking the tunnel for a week. On 1 August 1894, the new tunnel was passed for use by inspector Major Yorke. The opening of the double-track tunnel provided additional capacity for the L&NWR, allowing them to temporarily close the single bores for maintenance. As of 2018, excluding the London Underground, the double-track bore is the fifth-longest UK rail tunnel, after the High Speed 1 tunnels for the Thames Estuary and English Channel, the Severn Tunnel on the Great Western Main Line, and the Totley Tunnel on the Sheffield to Manchester route. Only the 1894 rail tunnel is in use but all three rail tunnels are maintained. In 1966, the 1848 single-track rail tunnel was closed followed by the 1871 single-track tunnel in 1970. The 1848 tunnel provides an emergency escape route for the other tunnels and has been made accessible to road vehicles such as fire engines and ambulances. Both the 1848 and 1871 tunnel are used by maintenance personnel for access. During the 2000s, Network Rail proposed reinstating rail traffic through the 1848 and 1871 tunnels to increase