Tinsley Viaduct is a two-tier road bridge in Sheffield, England; the first of its kind in the UK. It carries the M1 and the A631 1,033 metres over the Don Valley, from Tinsley to Wincobank, also crossing the Sheffield Canal, the Midland Main Line and the former South Yorkshire Railway line from Tinsley Junction to Rotherham Central. The Supertram route to Meadowhall runs below part of the viaduct on the trackbed of the South Yorkshire Railway line to Barnsley.
|Maintained by||Highways Agency|
|Design||twin deck box girder bridge|
|Total length||1,033 m (3,389 ft)|
|Height||20 m (66 ft) (to upper level)|
|Longest span||50 m (160 ft) (20 spans)|
|Clearance above||10 m (33 ft) (on the A631)|
|Clearance below||10 m (33 ft)|
|Construction start||Spring 1965|
|Opened||25 March 1968|
|Daily traffic||100,000 vehicles/day|
The viaduct was opened in March 1968 and cost £6 million to build. The structure is unusual in that it is built as steel box girders, at a time when most long span bridges were being built of post-tensioned concrete deck design. This use of steel allowed a significant cost saving over alternative methods, but became controversial after three serious disasters, when new bridges collapsed in 1970 (West Gate Bridge and Cleddau Bridge) and 1971 (South Bridge (Koblenz)). Fifty-one people were killed in these failures, leading in the UK to the formation of the Merrison Committee. The report of the Merrison committee resulted in the temporary closure of two of the carriageways on the lower deck and two on the upper deck, the installation of extra steel strengthening bands around the bridge's support columns and other works which were completed in 1983. A further program of strengthening was completed in 2006. The recent work to strengthen the bridge was a very complex operation, with a lot of the work happening inside the box beam spine. The works took over 3 years and cost £82 million (14 times the original bridge building cost). The strengthening project won the British construction industry's Major Project Award in 2005.
Although originally designed to carry a dual 3-lane motorway on the top deck, during and subsequent to the strengthening work the M1 was permanently reduced to 2 lanes following an EU directive on load bearing capacity to allow for the introduction of 40-tonne trucks in the UK. This arrangement allowed the third lane in each direction to join from Junction 34 to make the very busy junction safer. Since the opening of the M1 junction 32 to 35a smart motorway scheme in January 2017, the viaduct once again carries 3 lanes of traffic plus hard shoulders in each direction. 
The viaduct is balanced on rollers to allow for thermal expansion and contraction, and the route weaves slightly in order to make its way past obstacles. The viaduct, due to its construction, is very flexible. Movement may be felt on the lower deck as the traffic passes overhead. The Meadowhall Shopping Centre lies in the valley to the west; to the east is the Blackburn Meadows sewage works.
Tinsley cooling towersEdit
The viaduct is one of Sheffield's most prominent landmarks, and was once made all the more so by the adjacent pair of cooling towers that were left standing for safety reasons after the demolition of the Blackburn Meadows Power Station. The cooling towers were a major point of contention over the years and were once saved from destruction only after being chosen as a nesting site by a rare bird. More recently, plans were made to turn them into a piece of public art. Other plans for the towers included concert halls, skate parks and a theme park.
Their iconic status, and the possibly prohibitive costs of demolishing the towers safely, until recently looked to have cemented their status in Sheffield's future as much as they were a part of its history, until the owner of the towers (and the now-demolished power station) E.ON UK, stated its intention to demolish them once the strengthening of the viaduct made it feasible.
The 250 feet (76 m) towers were demolished at 03:00 BST on 24 August 2008 though a significant portion of the north tower remained standing for a short while. The demolition attracted widespread attention. A viewing platform was set up so the public could watch the demolition. Part of the site is proposed to be used for a new biomass power station by the owners E.ON UK.
In popular cultureEdit
The Tinsley Viaduct was 'ground zero' for a fictional Soviet Union nuclear strike on Sheffield depicted in Threads (1984), a depiction of what might have happened had NATO and the Soviet Union entered conflict over hypothetical instability in Iran, which escalated into full nuclear war. In the ensuing nuclear exchange, a one megaton nuclear missile detonates above the Tinsley Viaduct, devastating most of surrounding Sheffield.
- "Tinsley Viaduct". Highways Agency.
- "Safespan's Latest News". Safespan Inc.
- "M1 Aston-Sheffield-Leeds". The Motorway Archive Trust.
- "Tinsley viaduct strengthening project, Sheffield". Prime Minister's Award. Archived from the original on 5 December 2008.
- Leleux, Sydney A. (February 1969). "Tinsley Viaduct, Sheffield".
- Department of the Environment (Merrison Committee of Inquiry) (1973). Inquiry into the Basis of Design and Method of Erection of Steel Box Girder Bridges. London: HMSO.
- "£82 Million M1 Tinsley Viaduct strengthening work nears completion". Highways Agency. 2005-10-10.
- Template:Cite web?url=https://www.gov.uk/government/news/transforming-the-m1-in-yorkshire-and-the-east-midlands-find-out-more
- "Turning towers into art". BBC News. BBC. 8 July 2006.
- "August demolition date set for Tinsley cooling towers". E.ON UK. 2008-08-12.
- "Blast demolishes landmark towers". BBC News. BBC. 24 August 2008. Retrieved 2008-08-24.
- "E.ON UK Blackburn Meadows Green powerstation". E.ON. Retrieved 2008-08-24.