Welwyn Tunnels
| Welwyn Tunnels | |
|---|---|
The highly-decorated southern portal of Welwyn South Tunnel in 1951 The southern portal of Welwyn North Tunnel in 1951 | |
Interactive map of Welwyn Tunnels | |
| Overview | |
| Line | East Coast Main Line |
| Location | Digswell, Hertfordshire (Welwyn South Tunnel) Oaklands/Woolmer Green, Hertfordshire (Welwyn North Tunnel) |
| Coordinates | 51°49′41″N 0°11′24″W / 51.828°N 0.190°W |
| Status | Operational |
| System | National Rail |
| Operation | |
| Opened | 7 August 1850 |
| Owner | Network Rail |
| Operator | See East Coast Main Line § Operators |
| Technical | |
| Design engineer | Thomas Brassey |
| Length | North Tunnel: 1,046 yd (956 m) South Tunnel: 446 yd (408 m) |
| No. of tracks | 2 |
| Track gauge | 4 ft 8+1⁄2 in (1,435 mm) standard gauge |
| Electrified | 25 kV 50 Hz AC |
Operating speed | Down Main: 115 mph (185 km/h) Up Main: 105 mph (169 km/h) (South Tunnel); 125 mph (201 km/h) (North Tunnel) |
The Welwyn North Tunnel and Welwyn South Tunnel are two railway tunnels on the East Coast Main Line between Welwyn North and Knebworth railway stations in Hertfordshire, England. They are 1,046 yards (956 m) and 446 yards (408 m) in length respectively, with an 11-chain (730 ft; 220 m) cutting between them. They each consist of a single bore, forming part of capacity problems on that section of the East Coast Main Line. They tolerate a speed of 115 miles per hour (185 km/h) on the Down Main track; the speed on the Up Main track is 125 miles per hour (201 km/h) in the North Tunnel and 105 miles per hour (169 km/h) in the South Tunnel.
The tunnels were built in 1849–50 as part of the Great Northern Railway between London and Peterborough. The southern portal of the South Tunnel is highly decorated and was given Grade II listed status in 2000 alongside the adjacent Welwyn North railway station. In 1886, there was a three-way crash in the North Tunnel caused by a broken-down train whose driver did not follow correct procedures; it would later be described as "one of the most destructive in railway history". In the modern day, the tunnels are frequently discussed as part of capacity issues on the East Coast Main Line which limit the trunk route to only 18 trains per hour.
Design
Both tunnels consist of only a single bore, making them the closest tunnels to the terminus of the East Coast Main Line (ECML) at London King's Cross to do so. The nearest tunnels in either direction are the Potters Bar Tunnel, approximately 11 miles (18 km) to the south, and the Stoke Tunnel, approximately 73 miles (117 km) to the north. The South Tunnel is situated between 22 miles 11 chains (22.14 miles, 35.63 km) and 22 miles 31 chains (22.39 miles, 36.03 km) down the line from London King's Cross, from which distances on the ECML are measured, and the North Tunnel is situated between 22 miles 44 chains (22.55 miles, 36.29 km) and 23 miles 12 chains (23.15 miles, 37.26 km).[1] The southern portal of the South Tunnel is situated around 300 metres (980 ft) from the end of the platforms at Welwyn North railway station.[2]
The speed limit through both of the tunnels is 115 miles per hour (185 km/h) on the Down Main track; on the Up Main track, it is 125 miles per hour (201 km/h) in the North Tunnel and 105 miles per hour (169 km/h) in the South Tunnel. The speed limit on the Down Main track then increases to 125 miles per hour (201 km/h) immediately after the northern portal of the North Tunnel, marking the most southerly point on the line where the line reaches its maximum speed; this means that Knebworth railway station is the first through which trains may travel at this speed.[1] The gradient of the tunnels and cutting between is 1 in 200 (5‰).[3]
History
The engineers who designed the layout of the Great Northern Railway were William and Joseph Cubitt. The tunnels were built between 1849 and 1850,[2] and were the responsibility of Thomas Brassey, who constructed the line between Hornsey and Peterborough.[4] Services on the line began in 1850. The southern portal of the South tunnel, which is visible from Welwyn North railway station, was built from sandstone ashlar, as a semi-circular arch. The portal has towers on either side as well as a cornice and a parapet.[2]
On 9 June 1886, there was a major rail crash in the North Tunnel, which L. T. C. Rolt described as "one of the most destructive in railway history".[5] Initially, a fault with a Great Northern Railway locomotive led to it becoming stationary on the Down (northbound) track in the Welwyn North Tunnel. The guard wanted to move the train back to Welwyn railway station (now Welwyn North) by taking advantage of the falling gradient, but the driver refused as it was against the railway policy. The driver, however, did not take adequate steps to protect the train from a collision because it was stationary. As the tunnel was full of smoke from the broken locomotive, the next train did not notice it and hit it from behind. A third train, travelling southbound, then hit the debris from the collision which had covered both tracks; miscommunication between the signallers at Welwyn and Knebworth had meant neither were aware of the collision. There were two injuries and two deaths.[3]
Capacity issues surrounding the tunnels and nearby Digswell Viaduct have been raised since as early as the 1890s, when the Hertford Loop line was extended to Stevenage in order to prevent having to widen the viaduct from two tracks to four. The project was completed in 1898,[6] and the Hertford Loop line is still used as a diversionary route for trains today when there is disruption on the East Coast Main Line.[7] The Department for Transport's 2006 study on railway capacity raised the issue again.[8]
In August 2013, BBC News listed the idea of widening the viaduct and the adjacent Welwyn Tunnels to four tracks as one of the top five infrastructure projects that could improve life for people in the United Kingdom. It estimated the cost of such a project at £440 million and considered its likelihood to be "probable, at some point".[9] As of 2015 Network Rail set the maximum capacity of the bottleneck at 18 trains per hour (tph).[10] The East Coast Main Line 2016 Capacity Review considered the quadrupling of the viaduct and Welwyn North railway station, concluding it "would not fully resolve the capacity constraints", only increasing capacity for intercity trains by 2–3tph.[11]
The Welwyn North Tunnel is part of a Network Rail pilot program to investigate refurbishment of the deteriorating concentric brickwork of many Victorian era railway tunnels. Because the local geology renders it suitable for roadheaders and hydraulic picking as opposed to drilling and blasting, the ideal method is using a Tunnel Enlargement Machine; this reduces disruption by placing a shield inside the original lining and then excavating the original linings.[12] On 4 October 2000, the southern portal of Welwyn South Tunnel was given Grade II listed status, which complements that of Welwyn North railway station's footbridge and station building, listed on the same date.[2] As of March 2026, the operators passing through the Welwyn Tunnels include Grand Central, Great Northern and Thameslink, Hull Trains, London North Eastern Railway, and Lumo.[13]
See also
References
- 1 2 "London North Eastern Sectional Appendix" (PDF). National Electronic Sectional Appendix. Network Rail. pp. 206, 208, 218. 7 June 2025. Retrieved 6 December 2025.
- 1 2 3 4 Historic England. "South Portal of Welwyn Tunnel (1385392)". National Heritage List for England. Retrieved 29 March 2026.
- 1 2 Rich, Capt. Frederick Henry (22 June 1866). "Great Northern Railway". Accident Returns (PDF). Board of Trade.
- ↑ "The Story of Potters Bar and South Mimms" (PDF). Potters Bar and District Historical Society. 1966. pp. 67–68. Archived (PDF) from the original on 12 August 2024. Retrieved 6 December 2025.
- ↑ Rolt, L.T.C. (1976). Red for Danger. Pan. ISBN 0-330-25555-X.
- ↑ Phillips, Charles (6 March 2025). The Great Eastern Railway - From the Grouping to the Elizabeth Line 1923–2023. Pen and Sword Transport. pp. 20–21. ISBN 978-1036103606. Archived from the original on 10 May 2025. Retrieved 23 June 2025.
- ↑ Nick de Bois (28 January 2014). "First Capital Connect (Hertford Loop)". Parliamentary Debates (Hansard). Vol. 574. Parliament of the United Kingdom: Westminster Hall. col. 225WH–227WH. Archived 18 June 2025 at the Wayback Machine
- ↑ "APPENDIX 2: Issues in defining and measuring railway capacity" (PDF). Office of Rail Regulation. 13 February 2006. p. 2. Archived from the original on 6 April 2025. Retrieved 28 February 2014.
- ↑ "Could these five projects improve life in the UK?". BBC News. 13 August 2013. Retrieved 22 June 2025.
- ↑ "Is there a solution to the East Coast conundrum?". RailReview. 30 June 2025. Retrieved 29 March 2026.
- ↑ Review of Strategic Alternatives to High Speed Two (PDF) (Report). Network Rail. November 2011. p. 32. Retrieved 29 March 2026.
- ↑ Atkinson, Cameron; Paraskevopoulou, Chrysothemis; Miller, Richard (1 February 2021). "Investigating the rehabilitation methods of Victorian masonry tunnels in the UK". Tunnelling and Underground Space Technology. 108. doi:10.1016/j.tust.2020.103696. ISSN 0886-7798.
- ↑ "National Rail All Stations Route Map" (PDF). National Rail. 12 December 2025. Retrieved 14 March 2026.