The Scotsman has been at the forefront of the campaign pushing for a speedy decision on a crossing to replace the existing bridge, which has been weakened by corrosion.

The Scottish Government has chosen a cable-stayed crossing as a cheaper and quicker alternative to a tunnel.

Announcing the plan, ministers said the cost had risen by nearly £1 billion and they admitted several gaps remained over the details, such as how construction costs would be funded and who would control the crossing.

Opposition parties accused the SNP government of broken promises for failing to decide on some key aspects of the project. They fear the bridge will not be completed by 2016, as planned, because it is not yet known if potentially time-consuming new legislation will be required, and who will run the project.

Ministers said the price had gone up because the cost of including space for a tram line or separate busway had not been previously revealed.

John Swinney, the finance secretary, told MSPs the bridge would open "in around nine years' time" at a cost on completion of between £3.25 billion and £4.22 billion. Ministers previously said it would be £2.5 billion to £3.5 billion.

On funding, all he would say was that there would be no tolls on the bridge, and further announcements would be made next year.

The long-awaited decision comes a year after The Scotsman launched a campaign for an immediate commitment to a new crossing which was answered within weeks by the previous administration, who announced approval in principle.

The new Scottish Government pledged in June that decisions would be taken "in the autumn" on both the type of crossing and "on finance, legislation and governance".

The Scottish Liberal Democrats, who were accused by the SNP of dragging their heels on the project when in power a year ago, accused the Nationalists of hypocrisy.

Alison McInnes, their transport spokeswoman, said: "It is very concerning that the SNP have failed to answer fundamental questions, most notably on how they plan to pay for the new bridge.

"They promised answers by the end of the year, and this is another broken promise by the SNP government.

"There must now be serious doubts about the SNP's ability to deliver this project on time."

The Conservatives, who abandoned an almost identical project a decade ago, said much had still to be decided.

Murdo Fraser, the Scottish Tories' deputy leader, said: "We have finally got the type of crossing decided, but all the other big questions remain unanswered. There is an urgency now to put the rest of the pieces of the jigsaw in place if we have any chance of meeting the 2016 deadline."

However, the Scottish Government argued that it had set out the timescales for finance and legislative issues.

The cable-stayed bridge will be a similar type of crossing to the Kessock Bridge in Inverness and the second Severn crossing. It will have three pylons supporting its deck.

Mr Swinney said it could be built in five and a half years, six months more quickly, and more cheaply, than a suspension bridge like the Forth Road Bridge, because work could take place at several places at once.

It will be built just west of the existing road bridge, with a new road, some two miles long, connecting it to the M9. A much shorter road connection will be required at the north end.

The bridge will be a dual carriageway, with hard shoulders to cope with breakdowns and wind-shielding. It will also include a "multi-modal" element, a separate two-lane section that could be used by trams or buses.

A bored or immersed-tube tunnel further west was rejected on the grounds of cost and the likely environmental damage.

Mr Swinney said the impact of a bridge on the environment would be easier to mitigate.

A new crossing is required as corrosion of the main cables of the Forth Road Bridge could mean lorries being banned as early as 2013, with closure to all traffic six years later. Attempts will be made to halt the corrosion by blowing dry air into the cables from 2009, but there is no certainty it will work. The replacement or strengthening of the cables would be feasible, but would involve massive traffic disruption over several years.

No decision has been taken over its long-term future, but experts believe it will ultimately be repaired to help cut cross-Forth congestion, which is predicted to continue to grow.

Yesterday's decision was welcomed by business groups, but environmental campaigners said the existing crossing should be repaired instead.

Iain McMillan, the director of CBI Scotland, said: "We have consistently argued that a new Forth crossing is a need-to-do, rather than a nice-to-do, and a vital component of the new infrastructure investment that our nation so badly needs.

"The challenge now is for the government to get on with the construction of the new bridge as soon as possible."

Ron Hewitt, the chief executive of Edinburgh Chamber of Commerce, said: "We welcome John Swinney's statement. His grasp of the issues was salutary and his reasoning impeccable in preferring the cable-stayed bridge approach."

Gavin Scott, the Freight Transport Association's head of policy in Scotland, said: "

Our only concern is that the timescale indicated means the new bridge will not be complete for another nine years well past the time that the current bridge might be closed to large vehicles if the deterioration of the cables continues at the present rate."

Jenny Dawe, the Edinburgh city council leader, said: "It's especially encouraging to see the bridge will include an element of future-proofing, with the capacity to accommodate additional light rail transport such as trams or a guided busway."

But Duncan McLaren, the chief executive of Friends of the Earth Scotland, said: "If ministers are to deliver both their economic and climate-change goals, they must concentrate on fixing the existing road bridge rather than pursuing any additional crossing."

Projected costs and timescale for the crossing

It is estimated that the new bridge will cost between £3.25 billion and £4.22 billion

Further details about the bridge and how it will be approved and built will be announced next year

Plans will be submitted for authorisation in 2009

A competition for building the bridge will be staged in 2010

A constructor will be appointed in 2011

The bridge is expected to be open in 2016

There were four options considered for the crossing featuring two types of tunnels and two bridges

The final design will be a cable-stayed bridge, and three pylons or towers, with cables bracing the decks of the road

The central tower will be located on Beamer Rock

This will incorporate two main spans of 650 metres each with equal back spans of 325 metres

The bridge will be sited just west of the existing road bridge

The option is considered to be both the cheapest and quickest with a construction time of five-and-a-half years

There will be a dual two-lane carriageway with hard shoulders and pedestrian and cycle access

Two separate lanes for public transport, such as trams or buses will be designed.

It is expected that the new link will reduce the CO2 emission generated by the current crossing

The cost of dedicated public transport for the bridge is £452 million

Provision will be made to allow for the introduction of a light rail or guided bus system

The modern design means the crossing should remain open even during high winds

Funding options for crossing take a new direction

FUNDING of one of Scotland's largest ever building projects is one of the most significant unanswered questions about the new bridge.

The Scottish Government is expected to announce details today of its proposed Scottish Futures Trust, which is seen as a non-profit alternative to previous private funding methods for public projects.
However, all John Swinney, the finance secretary, would say yesterday was that private sector involvement would not be ruled out.

It is thought the trust is likely to involve a partnership between government bodies and firms, but with any profits going to the public purse rather than shareholders.

An alternative would be traditional funding, where the government is able to borrow money at lower interest rates to pay for schemes.

Mr Swinney said: "Work is continuing on the procurement options and this will include consideration of the appropriate risk to the private sector, in line with current government policy on the development of the Scottish Futures Trust. The government is against tolling."

However, he admitted the scale of the project would have a major impact on government coffers. He said: "This will put a significant strain on other projects during this period."