page_title: Severn Tunnel
section_title: Operations
hierarchical_section_title: Severn Tunnel / History / Operations
caption_attribution_description: English: Severn Tunnel from the Welsh side
context_page_description: The Severn Tunnel is a railway tunnel under the Severn Estuary between England and Wales.
  The tunnel links South Gloucestershire in the west of England to Monmouthshire in south Wales. It was constructed by the Great Western Railway between 1873 and 1886 to shorten the journey between Western England and South Wales. Its completion has been regarded as the crowning achievement of the civil engineer Sir John Hawkshaw, the chief engineer of the GWR.
  Before the Severn Tunnel was built all traffic between Western England and South Wales was by ship or upriver via Gloucester. The single-track Severn Railway Bridge, 14 miles upstream, opened during the construction of the tunnel. Recognising the value of a tunnel, the GWR tasked Hawkshaw with its design and the civil engineer Thomas A. Walker to undertake its construction, which commenced in March 1873. In October 1879, the works were flooded by what is now known as "The Great Spring". Through strenuous and innovative efforts, the flooding was contained and work continued, albeit with a great emphasis on drainage.
context_section_description: At Severn Tunnel Junction station, the GWR built a marshalling yard, which distributed coal from the South Wales Valleys towards London and the Midlands, created mainline and local mixed-traffic freight from goods shipped in from the Midlands, the Southwest and along the Thames Valley into Wales and vice versa.
  Because of the tunnel's access gradients, (eastwards, from Severn Tunnel Junction): 3 ¹⁄₂ miles (5.6 km) at 1 in 90 (1.11%) down to the middle of the tunnel; a further 3 ¹⁄₂ miles (5.6 km) at 1 in 100 (1%) up to Pilning; a short level then 3 ¹⁄₂ miles (5.6 km) at 1 in 100 (1%) up to Patchway, throughout the steam era, assistance was required for heavy trains. The locomotive shed at Severn Tunnel Junction (86E), had a number of pilot and banking locomotives to assist trains through the tunnel. Pilot locomotives usually worked eastwards and were detached at Pilning, and worked westwards piloting a second train back to the marshalling yard. Under British Rail the locomotives were usually GWR 5101 Class 2-6-2T locomotives, the bulk of which form the core preserved stock of that class.
  Fixed Cornish engines with Lancashire boilers used to pump water from the Great Spring and other sources of water were in use until the 1960s, when they were replaced by electrically powered pumps. The pumps and control systems have since been replaced in the 1990s by Railtrack. During the 1930s, the reliable fresh water supply from the Great Spring was a factor in favour of the selection of an adjacent site for the Royal Navy Propellant Factory, Caerwent. Water was also supplied to a paper mill at Sudbrook which has since been closed.
  The Severn Tunnel rail accident occurred on 7 July 1991. An InterCity 125 was struck from behind by a Class 155 Super-Sprinter. The accident investigation, while unable to reach a firm conclusion, indicated that the axle counters used for detecting train movements in the tunnel may have been accidentally reset.
  The Second Severn Crossing, built in the 1990s, crosses the tunnel on a "ground level bridge" on the English side, near the Salmon Pool. The bridge is supported so that no load is imposed on the tunnel. During that bridge's construction, the concrete cap above the tunnel in the Salmon Pool was renewed.
  In 2002, two Class 121s were overhauled by LNWR for use as a Network Rail tunnel emergency train. These were stabled to the west of Severn Tunnel Junction station but only used in training exercises.
caption: A High Speed Train enters the Severn Tunnel from the Welsh side.
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