SUSPENSION cables holding up the old Severn Bridge are rusting and snapping - and engineers have no idea how much long term repairs will cost the taxpayer.

At a press conference today, it was revealed that tests on the bridge - 40-years-old last September - have identified "significant corrosion" in up to 50 percent of the 8,322 wire strands which make up each of the load bearing cables - and more than 160 wires were found to be actually broken. Less serious corrosion and wire breakages are also affecting cables near the main towers.

Highways Agency chiefs say that despite the findings the bridge is still safe and there are no plans to close it.

But they are embarking on a £27 million package of further tests and measures aimed at halting the rot until engineers decide how to repair the defects.

Meanwhile, new lorry weight regulations restricting heavy trucks to lane one in each direction are being introduced and should in place by Easter.

A £1million accoustic monitoring system is being installed to listen for further possible cable breaks and a dehumidification system - ultimately costing more than £20million - is also being introduced, initially on the worst affected sections, to limit further deterioration.

Highways Agency project director Patrick Carney said the worst affected cables were in the middle section of the bridge where stresses were lowest.

"Safety is our strongest priority and based on our current findings there is no reason to close the bridge," he said. "However, we are still investigating he full extent of the corrosion and its implications."

Mr Carney said cable corrosion was proving to be an inherent problem with suspension bridges of similar design worldwide including the United States. In Japan it had been found in a bridge just four years old.

Engineers all over the world were working to find cost effective solutions and no decisions had yet been made on full scale repairs needed for the bridge to achieve its intended 120 year lifespan.

"Many repair options already exist but it is far to early to say what will be considered suitable here." said Mr Carney. "All things are possible. It could ultimately be a decision for the Secretary of State but I am confident that the Severn Bridge will still be open after 120 years."

The high costs will not drive up toll charges - currently £5.10 for cars - which are set by legislation.

Built at a cost of £8million the bridge which now carries the M48 motorway to Chepstow and is operated by a private company, Severn River Crossing plc, under a Government concession.

The firm will escape the repair bill because the risk of serious defects was not part of the transfer agreement.

The M4 Second Severn Crossing which opened almost 11 years ago, now accounts for 75 percent of total traffic across the river. The old bridge carries around 17,000 vehicles a day, including 3000 heavy goods vehicles.

The condition of the cables will not affect the protocol for closing the bridge during high winds.

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