The main suspension cables on the Forth Road Bridge can be strengthened or replaced - but it will mean years of traffic delays, according to a report.
One of the options is to replace the bridge towers and cables
The preliminary findings of the Main Cable Replacement Study has provided the Forth Estuary Transport Authority (Feta) with three options.
Two of the options would mean the bridge being closed completely every weekend for almost a year.
The third would mean disruptive roadworks but no closures.
The report said the problem with the third option, which would involve adding new towers and cables over five-and-a-half years, was that it may not provide sufficient strength.
It said replacing or augmenting the cables would be the last resort if current moves to dry them out failed.
However, this will not be known for four or five years.
The first option would be to remove and replace the cables. However, that would mean bridge closures every weekend for almost a year and the introduction of a contraflow system for several weeks.
The whole project would take seven years.
The second option would involve new cables being laid on top of the existing ones - also meaning a year of weekend closures and lengthy lane restrictions.
This option would take six years.
The bridge authority said the report did not alter its case for a new crossing.
A survey of businesses will be carried out to establish the likely economic impact, and further work will be carried out to develop a local traffic model.
Feta general manager and bridgemaster Alastair Andrew said: "The replacement or augmentation of the main cables on the Forth Road Bridge presents significant engineering challenges, but we have now confirmed that it is technically achievable.
"The big question was always the impact of the traffic restrictions required to carry out the works safely, and it is clear that these would result in significant delays to the strategic roads network over a number of years.
"The impact of one carriageway closure can be compared to the current weekend restrictions for carriageway resurfacing."
He said current delays are about 60-90 minutes, even with 30% less traffic than usual.
"Significantly more vehicles use the bridge during the week than at weekends, so continuous carriageway closures Monday to Friday would cause significantly greater delays," he said.
"It must be emphasised that this is only a preliminary report and further detailed analysis may result in changes to the options and timetable."
He added that a comprehensive report was due at the end of the year with a further analysis to be carried out between January and April 2008.
The report has been submitted to the transport minister to inform the decision-making process for the new Forth crossing.