A study by the Forth Estuary Transport Authority (FETA) found that the current bridge is operating close to capacity and could be forced to close by 2013. It uncovered "irreversible" corrosion in the bridge's main cables.
Scott insisted that the bridge is safe and able to carry traffic. But he admitted that FETA has found corrosion and conceded the need to assess the extent of the damage and the work that must be done.
The study should be complete by summer 2007, while the Scottish Executive will consider the broader issues of travel across the Forth in 2006, Scott added.