The Bletchley Flyover is a railway viaduct that crosses the West Coast Main Line (WCML) just south of Bletchley railway station in Milton Keynes, England. It was originally a reinforced concrete railway viaduct that carried the former Varsity line between Oxford and Cambridge from 1959 until its closure in 1968. The flyover was retained, but largely unused until 2021, when the East West Rail Alliance demolished then rebuilt the structure. It reopened for engineering use in early 2022.

The original structure was composed of 37 concrete spans, resting on concrete piers. It is 605 metres (1,985 ft) long. Most of the spans are beam-shaped; two are double-length arches. Electrification pads were provided when the flyover was first built, despite there being no plans to electrify the line.

In 1959, the Bletchley Flyover was opened to carry the Varsity line over the West Coast Main Line (WCML) as part of the British Rail Modernisation Plan. The plan proposed to develop the Varsity Line as a freight link from the East Coast ports to South Wales, capable of handling up to 2,400 wagons of coal class traffic and empties daily. However, following British Railways deciding not to proceed with the Swanbourne sidings plan, the line saw little use, with most freight traffic taking other routes.

The Varsity line closed to passengers on 1 January 1968; it remained open to goods traffic until October 1993, when the bridge was mothballed. The flyover was returned to use in 2006 along with a mile of track west of Bletchley to a loop at the Newton Longville Brickworks landfill site.

As part of the East West Rail project that will reopen the Oxford – Cambridge route, work to replace 14 of the spans began in April 2020. Sections beside and over the WCML were removed in April and May. The arches crossing Buckingham Road (on the east side of WCML) started being removed on 5 July 2020. "The final span was lifted out by crane in October and the last of the supporting piers and pillars were removed over the weekend of 9-10 January 2021". At the early May 2021 holiday, 103 concrete girders were lifted into place to provide the bridge deck over the main line.

During summer 2021, a new structure was built for use by East West Rail, in the form of a box tunnel around the WCML; by February 2022, 1.5 km (0.93 mi) of track had been installed over the new flyover, enabling engineering trains to reach the eastern end of the construction site.

The renovation project includes a plan to construct high level platforms for Bletchley station, just after the eastern end of the flyover. These platforms will serve East West Rail (only).

v t e Stations in and around Milton Keynes
Legend
West Coast Main Line towards Glasgow Central Northampton loop to Northampton Roade Bedford–Northampton line towards Northampton Stratford-upon-Avon and Midland Junction Railway Salcey Forest Hanslope Junction Castlethorpe Olney Wolverton and Stony Stratford Tramway towards Bedford Deanshanger Old Stratford Wolverton–Newport Pagnell line Stony Stratford Newport Pagnell Wolverton Works Great Linford Wolverton Bradwell East West Rail / Marston Vale line to Bedford Woburn Sands Milton Keynes Central Bow Brickhill Denbigh Hall Fenny Stratford Bletchley TMD Bletchley with planned high-level platforms former Varsity Line / planned East West Rail to Oxford Bletchley Flyover Leighton Buzzard West Coast Main Line towards Euston

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