The M1 viaduct at Tinsley, almost on the boundary between Sheffield and Rotherham, was an adventurous solution to a complex engineering problem – a double-deck design, taking the motorway on the top deck and a trunk road beneath across a flat valley-floor site riddled with old mine-workings, circumventing an electricity generating station and a sewage works and crossing two railway-lines and two main roads.
The M1 deck is 65 feet above the valley-floor; the A631 trunk road is slung twenty-five feet below it.
Colonel Maynard Lovell, the highways engineer of the West Riding County Council, submitted an original design in concrete, built in sections to counteract subsidence and heat-expansion: its estimated cost was £6 million.
This proposal was overruled by the Transport Minister, Ernest Marples, in favour of a single-unit steel box-girder design by Freeman Fox & Partners costing £4.6 million.
The viaduct, Junction 34 of the M1, opened to traffic in 1968 – the lower deck, carrying the A631, in March and the upper motorway deck in October.
Within the following three years three box-girder bridges collapsed, causing fatalities, while still under construction.
In 1970 the Cleddau Bridge at Milford Haven killed five workers and the West Gate Bridge over the Yarra River in Melbourne, Australia, killed thirty-five. In 1971 the South Bridge over the River Rhine at Koblenz in West Germany also collapsed, killing thirteen.
The Cleddau and Yarra bridges were both designed by Freeman Fox & Partners, who in the same decade designed the first Severn Bridge (1966) and the Humber Bridge (1980).
It may have seemed appropriate to have a steel viaduct bridging the industrial heartland of the city of steel, but the original flexible concrete design would have avoided the disadvantages of the insufficiently tested box-girder construction, and a concrete viaduct doesn’t need painting.
However a 2004 Highways Agency calculation indicated that replacing as opposed to rebuilding the viaduct would cost £200 million and involve hidden costs for delay and disruption amounting to £1.4 billion.
Initial modifications to Tinsley Viaduct began in February 1976 and continued with few interruptions for years. The additional cost was given as £3 million at the start of the rebuilding programme.
The ugly cross-girders and diagonal reinforcements along the lower deck have destroyed what elegance the original structure had, and their installation in a structure carrying an operational trunk motorway was a logistical nightmare. The original maintenance gantries had to be completely redesigned, and the previously unrecognised need to inspect the inside of the box-girders required the fitting of permanent lighting and safety rails. Furthermore, the formerly sulphurous atmosphere of the East End steelworks necessitated frequent repainting (£2 million at 1980 prices).
An £81,000,000 scheme to strengthen the structure further in order to meet EU criteria was completed in late 2005: European legislation had restricted the motorway to four lanes; intricate internal reinforcement of the box-girders enabled it to carry 40-tonne vehicles over six lanes and permitted a safer configuration of the Junction 34 slip roads.
It’s difficult, because of the effects of inflation, to ascertain whether the patching of the Tinsley Viaduct was in the end cheaper than knocking it down and building a new one.