THE Forth Road Bridge is not deteriorating as quickly as feared, meaning a ban on lorries using the crossing should not be necessary until 2017 at the earliest – three years later than expected.
A new inspection report from the Forth Estuary Transport Authority (FETA) indicates the bridge's main suspension cables have now lost about ten per cent of their strength due to corrosion.
In 2004, the first internal inspection of the 44-year-old bridge found an eight per cent loss of strength and warned weight restrictions might need to be introduced some time between 2014 and 2020.
A Scottish Executive study soon afterwards warned a ban on HGVs could be necessary as early as 2013, with possible total closure of the bridge six years later.
But, following the latest inspection in February and March this year, FETA's consulting engineers FaberMaunsell are optimistic the rate of deterioration is at the "slower end" of expectations.
If efforts to halt the corrosion fail, they say it is more likely weight restrictions would be needed some time between 2017 and 2021.
The latest projections give breathing space to those in charge of building the new Forth Road Bridge approved at the end of last year.
Preparation work is already under way, but construction is not due to start until 2011, with completion scheduled for 2016.
The inspection involved taking samples of the thousands of individual wires that make up each cable and carrying out laboratory tests, including tensile tests, chemical analyses and corrosion analyses.
Barry Colford, FETA chief engineer and bridgemaster, said: "The good news is that, although the cables are still losing strength, the worst case scenario of an HGV ban in 2014 now looks unlikely."
A dehumidification system is currently being installed on the bridge in a bid to prevent further corrosion.
Mr Colford said: "The bridge's long-term structural integrity also depends on the outcome of precautionary checks on the bridge's anchorages, and we won't know the results of this work until 2011/12 either."
The full article contains 354 words and appears in Edinburgh Evening News newspaper.
