The total economic costs of undertaking the work whilst no alternative crossing is in operation are assessed at £1.3 billion.
A report from the Forth Estuary Transport Authority, to be considered by its board on February 22nd, estimates that the work would take between 7 and 9 years. It assesses the costs of three options for the repairs which were identified in a preliminary report in July 2007.
Implementing one of these would be necessary to extend the life of the bridge should current work to dry out the original cables fail.
Replacement of the cables with new main cables above the existing cables with capacity to carry all loads, option A, would be the most expensive at £122 million. The existing cables would subsequently be removed.
If new main cables were constructed above and the existing cables subsequently retained and the load shared , option B, the cost would be £120 million.
Option C would involve augmentation of existing cables with new cables to the side and load sharing and would cost £91 million.
Traffic modelling analysis suggests that the cost of travel delays from weekday closures of the bridge for the work would be significantly higher if option A were chosen at £335 million. Under option B it would be £238 million and under option C it would be £212 million.
Since the study was begun the Scottish Government has confirmed that a second Forth crossing will be built with a current expectation of completion by 2017. The results of the current cable drying process should be known by 2013.
A new crossing over the Forth was confirmed in December.