The bridge which transports 24 million vehicles every year across the Firth of Forth is celebrating its 40th birthday.
The bridge transports 24 million vehicles every year
It comes as operators of the Forth Road Bridge are resuming major roadworks, which will run every weekend for the next two months.
The bridge was built to provide a link between Fife and southern parts of Scotland.
It is being strengthened to deal with more traffic - as it carries twice as many vehicles as it was designed for.
The work was suspended for two months to prevent traffic jams during such annual events as the Royal Highland Show at Ingliston and T in the Park.
At 1800 GMT on Friday, the bridge was reduced to one lane in each direction as work commences on resurfacing the southbound carriageway.
Opinion has been divided on whether there should be another bridge beside the existing one.
The cost of a new bridge has been estimated at about £400m.
The price would be dependent on design and the incorporation of a tram link, while the construction of a rail link would increase it to about £580m.
The figures were included in a consultants' report on the feasibility of building another bridge.