MOTORISTS will face six months of severe disruption on one of the main bridges across the Clyde as it undergoes a £6 million safety upgrade.

Lanes will be closed causing severe tailbacks for the 35,000 vehicles that use the Erskine Bridge each day, to allow barriers strong enough to withstand the impact of lorry crashes.

The crossing, built in 1971, is currently undergoing a £3.5m programme to install safety barriers to try to prevent suicides, following the deaths of teenagers Neve Lafferty and Georgia Rowe in 2009.

A further £6m of work is due to start to replace the barriers either side of the central reservation by June. The work is expected to cause severe tailbacks for motorists who use the crossing between Erskine in Renfrewshire and Old Kilpatrick in West Dunbartonshire.

Transport Scotland, the Government agency responsible for trunk roads and motorways, said "high containment" barriers were required to protect the towers and cable anchorages in the central reservation which hold up the bridge.

A spokeswoman said the existing barriers are strong enough to withstand a car crash, but not an impact from a lorry.

The extent and exact timing is unlikely to be confirmed until a contractor has been appointed.

The contract published by Transport Scotland reveals that "continuous lane closures" will be needed during the works.

The notice states: "Extensive traffic management involving continuous lane closures and associated traffic diversions will be required to enable safe implementation of the works."

Engineering experts said the improvement work was unlikely to have been triggered by specific safety fears but ordered in response to changes in design standards.

Phil Flanders, the Road Haulage Association's director in Scotland and Northern Ireland, said the bridge was designed when lorries weighed far less.

"It was designed in the 1960s and when the heaviest lorries were normally 32 tonnes and abnormal loads were not such a problem. Now lorries are up to 44 tonnes," Mr Flanders said.

Transport Scotland's spokeswoman said traffic management plans would be put in place once the contract was awarded.