The Forth Road Bridge
's top engineer raised the alarm about the crossing 10 months ago, according to confidential papers.
"Phase three covers the demolition and replacement of Norham Road Bridge
, which is more than 50 years old and in need of urgent attention.
CLOSED Forth Road Bridge
has been shut for repair job
A City of Cardiff Council spokesman said: "The City of Cardiff Council has carried out an extensive public information campaign to notify motorists of the alternate route, following the closure of Windsor Road Bridge
by Network Rail.
"The bridge has stood on the site for 150 years and has come to the end of its life and we have come to the conclusion we have no option but to close the road bridge
with immediate effect."
DENIALS from Nicola Sturgeon and her Transport Secretary that cuts in the Forth road bridge
's repair's budget had anything to do with the failure now causing travel chaos for a large swathe of Scotland sound rather hollow.
Network Rail says Windsor Road bridge
, near Cardiff Prison, was built more than 100 years ago and is past its use by date.
The Pont Brewit road bridge
is alongside Pont Brewit railway bridge which is itself due to be closed until 2015.
He said: "If there is no increase it is estimated that the management, maintenance and operation of Forth Road Bridge
would result in an estimated debt of pounds 29.17m by 2018.
Clackmannanshire Council leader Keith Brown said: "The Forth Road Bridge
is operating above capacity.
Councillor Ramesh Patel, Cabinet Member for Transport, Planning and Sustainability, said: "Replacement of the Windsor Road bridge
is an essential improvement which will provide an updated structure to accommodate modern vehicles as well as permitting the eventual electrification of the main rail line.