Urgent calls are being made to upgrade the ageing M1 Tinsley Viaduct - before high speed rail plans mean it may never be replaced.
Sheffield Council and MPs fear the 45-year-old double-deck structure, which carries the motorway and junction 34 across the Lower Don Valley, will deteriorate to the point it has to be rebuilt one day.
They want the Government to act now since replacing the viaduct in the future will be more complicated as the HS2 rail line is planned to go alongside it – meaning there would be no space for a new one.
The Highways Agency, which manages the M1, said today the viaduct is in ‘serviceable condition’ and there are no plans to replace it.
But Sheffield South East Labour MP Clive Betts warned: “It would be a massive problem if the viaduct was to fail in future, and we need to be prepared.
“There has been ongoing maintenance of Tinsley Viaduct ever since it was built, and it has a history of problems.
“It would be better to be safe than sorry.”
Sheffield Council also says the Department for Transport needs to act now to ensure any project is not impeded by plans for the HS2 high speed rail line, which is set to cross the Lower Don Valley on a viaduct parallel to the motorway.
Coun Leigh Bramall, the council’s cabinet member for business, skills and development, said: “We need to act now to ensure that, in the future, if the viaduct does need replacing or expanding, there is space to build a new bridge.
“It is hugely important not only for Sheffield but the north of England as a whole.”
Construction of the viaduct began in the spring of 1965, and the £6 million structure - the UK’s first two-tier road bridge - opened in March 1968.
But Coun Bramall said replacement of the viaduct should now also be considered because of ‘capacity issues’ with the current structure, which has only two lanes open in each direction.
A third lane on either carriageway is currently closed to reduce wear on the steel structure.
Coun Bramall said: “With the M1 being widened to four lanes in each direction elsewhere, Tinsley Viaduct is a bottleneck. We should look at that issue, too.”
Options for replacement could include setting aside land between the existing M1 and the site of the rail viaduct, or even incorporating the motorway on the rail structure.
Building a new viaduct on the Rotherham side of the M1 would be difficult because of the sewage works and a power station which is under construction.
Any option could cost hundreds of millions of pounds because the motorway would have to be realigned on approach to the viaduct and junction 34 rebuilt.
Surrounding homes and businesses could have to be demolished.
Richard Wright, executive director of Sheffield Chamber of Commerce, who said: “The Tinsley Viaduct is such an important structure and we need a permanent solution.”
A Highways Agency spokeswoman said: “We will continue to carry out maintenance to ensure the viaduct remains in a safe and serviceable condition for many years to come.”
The agency added there would be ‘sufficient space’ between the existing viaduct and HS2 line to rebuild if necessary, but it has no plan at present.