Work has begun on a second road bridge over the Firth of Forth at Kincardine in a drive to ease traffic congestion.
The new bridge will be "slim and elegant"
The new link will be ready by 2008 and was commissioned because the existing bridge was carrying more traffic than it was designed for.
Local residents should see traffic reduction as the majority of vehicles will move away from Kincardine.
Dave Hill, project manager for the crossing, said it would be a "lovely looking, slim and elegant bridge".
The 1,200 metre link will allow repairs to be made to the existing bridge before the two operate together.
The existing bridge, which was opened in 1936, carries well over its design capacity and engineers have warned it would have to close for at least a year for major refurbishment.
The new crossing will be built just upstream of the old one and take the vast majority of traffic away from Kincardine itself.
Through-traffic has already been reduced with a new bypass and is expected to drop even further from more than 16,000 vehicles a day to just under 3, 000.
Campaigners opposed to road projects have accepted the need for a new bridge but they argue it should mean ruling out a second Forth Road bridge at Queensferry.
The new route will start from Bowtrees roundabout at the end of the M876 near Falkirk.
Speaking on BBC Radio's Good Morning Scotland programme, Mr Hill said: "It will stretch some 1.2km diagonally upstream of the existing bridge.
"As a construction project it's very interesting because it's a push-launch bridge and will be the longest of its kind in the world.
"Once we are constructing the piers across the river, we will cast the concrete deck on the north side, on the bank.
"Then inch by inch we push it with large rams across the river 1.2km, at which time when it reaches the far side it's weighing in excess of 35,000 tonnes."
Mr Hill said the crossing would be dual carriageway approaching from the M876 and then three lanes across the bridge.
"The new bridge will take the north and the west and the old bridge will take the east traffic," he added.
The project is intended to ease the burden on the existing bridge
Transport Minister Tavish Scott said: "This is a world-class project, vital for both the national economy and for communities in Kincardine.
"The bridge will further improve transport links in the Forth Valley and central Scotland and will help relieve traffic congestion for people in Kincardine and the surrounding area.
"It will also improve air quality and reduce traffic noise for local residents."
The National Alliance Against Tolls Scotland (NAATS) said while most people would welcome the new bridge it was "inadequate".
NAATS co-ordinator John McGoldrick said: "The authorities have said that the Forth road bridge may be closed to either lorries or all traffic due to cable corrosion.
"We don't believe this is likely, but it would have been prudent to make sure that the new bridge at Kincardine could take as much traffic as possible.
"We hope that the people do not regret the decision not to take the opportunity to build a bigger bridge."
Local historian Bill Woolsey said residents welcomed the second bridge as traffic through Kincardine was "extremely high".