Linslade Tunnel

Linslade Tunnel is a railway tunnel in Bedfordshire, England (in an area that was historically in Buckinghamshire), on the West Coast Main Line about 0.54 mi north of Leighton Buzzard railway station and built under Linslade Woods. Consisting of three individual bores, the tunnel is somewhat unusual as there is a slight bend in its alignment.

The first bore was constructed during the 1830s, the engineering of which having been performed by the pioneering railway builder George Stephenson. The only of the three bores to accommodate double track, it was first opened to traffic during 1837. During 1857, the eastern bore was opened to serve a branch line from Leighton Buzzard to Dunstable; this has since been closed. In 1876, the western bore was completed, being noticeably narrower than its predecessors. During the 1960s, Linslade Tunnel was outfitted with overhead electrification as part of a wider scheme to introduce electric traction on the West Coast Main Line. In the 1970s, the tunnel portals on either side of the tunnel were recognised as Grade II listed buildings due to their connection to early railway engineering history. During the 2010s, remedial engineering works were performed in the tunnel.

Design
The London and Birmingham Railway was opened in 1837. Robert Stephenson, the railway's chief engineer, was determined to keep the gradients on the route to a maximum of 1:330 which required significant engineering works. From the end of Tring Cutting to just south Leighton Buzzard railway station, the railway is carried on a series of embankments, after which it enters another deep cutting before reaching a small patch of sandstone high ground under Linslade Woods. A generation earlier, the Grand Junction Canal avoided the same obstacle with a sweeping curve to the east, adding route miles and decreasing speeds—both of which were undesirable, so Stephenson opted to tunnel through it.

The tunnel consists of three bores; the central bore was the first to be constructed and opened with the line in 1837. The contract for its construction was issued around 1834, one of the first contracts on the route. The central bore is 272 yd long and was built wide enough to carry two tracks. It has a depth of roughly 55 yd, its excavation involved the removal of 20,433 cubic yards (15,600 m3) of spoil. The tunnel was built on a slight curve. Around the time of its opening it was described as relatively spacious. Both of the additional bores are single-track width and were built on either side of the original. That on the east side was opened in 1859 and the western bore was added in 1875.

The tunnel portals at the northern end are heavily decorated. Above and around the openings is a red-brick retaining wall, except for the westernmost (the last one to be built) which is in blue brick. Above these is a blue-brick crennelated (castellated) parapet and a series of turrets flank the mouths of the portals. This use of blue brick suggests that the castellation was renewed when the westernmost tunnel was bored. The south portals are less elaborate but still decorated. They have significant batter (a sloping wall), rusticated voussoirs at the mouths and a rolled cornice above.

History
During the 1960s, Linslade Tunnel, along with the majority of the West Coast Main Line, had overhead electrification apparatus installed, which facilitated the line's transition to electric traction.

On 9 December 1982, during the British Rail era, there was a fatal incident at Linslade Tunnel: an inadequately secured load had fallen from one train and was struck by the next train passing through the tunnel, causing its derailment and the death of its driver.

During the late 2010s, deteriorated parts of the brickwork within Linslade Tunnel were repaired. In early 2020, there were more engineering works in the tunnel, largely focused on a comprehensive track renewal, to improve service reliability.

Both portals are Grade II listed buildings. The north portal is cited as an "interesting example of early railway architecture". The south portal, although less intricate, is included for completeness.