London And North Western Railway 1846-1923
Linslade Tunnel has 3 holes called bores. The middle bore dates from 1837 when the London and Birmingham Railway was constructed. The east bore was opened in 1859 when the new relief line was built and the station moved. As traffic on the line increased a fourth track was needed and this resulted in the construction of the third and final bore which was opened in 1876. This last bore is the narrowest of the three and can cause a lot of turbulence when a train goes through it at high speed.
This is the south (Leighton) end of the tunnel
This is the north (Bletchley) end of the tunnel