A new cut-price Forth crossing has been announced by the Scottish Government as it outlined its transport vision for the next 20 years.
The cost of the toll-free bridge, previously estimated at £4bn, has been reduced to between £1.72bn and £2.34bn.
Holyrood ministers want to publicly fund the crossing by bringing capital investment forward.
Labour claimed the move showed the SNP's alternative to PPP/PFI funding had failed.
Transport Minister Stewart Stevenson said the planned transport vision, which takes in 29 projects, was the most ambitious of its kind in Scotland.
It included plans to improve roads and train services across Scotland, but opposition MSPs questioned how much of it would actually happen.
Under government plans, the existing Forth road bridge would remain open for public transport, cyclists and pedestrians alongside the new one, due for completion in 2016.
Holyrood ministers have approached the Treasury about increasing the capital budget to fund the new crossing while it was being paid for, with a reduction in later years.
However, the Scottish Government has yet to receive an answer.
Mr Stevenson told parliament the new Forth bridge would dominate the investment programme until it opened, while warning parliament that the financial climate had "materially changed".
This, he said, included an estimated £1bn being taken from the Scottish budget between 2010 and 2012 in the wake of the chancellor's pre-Budget report.
"There are external factors outwith this government's control which will have an impact on how and when we can deliver on the infrastructure investment this country needs," said Mr Stevenson.
"There is continuing uncertainty in the financial markets. The cost of borrowing and the availability of funds are fluctuating daily."
The minister described the new Forth bridge, to be constructed through a conventional design-and-build contract, as a project of unprecedented recent scale.
He went on: "Our strategy is economically sound and a value for money solution. It meets every requirement and maximises use of our existing assets."
Labour transport spokesman Des McNulty said the Scottish Government had been humiliated by a decision not to use its Scottish Futures Trust (SFT) alternative to tie-ups with the private sector.
The transport plans, Mr McNulty said, were a "cruel con", with many projects destined never to be delivered.
He went on: "The new crossing was the acid test for the SFT. Its failure imposes a huge burden on the capital budget in the period during which this project will have to be paid for."
Alison McInness, the Liberal Democrat transport spokeswoman, said SNP ministers had been "poor custodians" of projects already in the system before they came to power.
And she accused ministers of inflating the price of the new Forth crossing in the first place, adding: "What possible confidence can we have that the government is up to the task in delivering this vital transport link."
Green MSP Patrick Harvie claimed "vanity" was a driving force behind many of the proposed projects that were planned.
"Ministers, I think of any political party, love the idea that they can stand there cutting a ribbon, wearing a hard hat, having their photograph taken smiling and thinking 'this is what I built, look what I did, aren't I a big strong minister'.
"I think this objective has marred transport policy for far, far too long."
The Conservatives' Alex Johnstone said the transport plans fell short of what was expected.
He told MSPs: "It falls short of delivering a true list of priorities. It falls short of delivering true budgets and, above all, it fails to deliver an adequate timescale."
Under the overall plans, Glasgow to Edinburgh rail journeys would increase to 13 services an hour by 2016, with the journey time cut to about 35 minutes.
The number of trains from Glasgow and Edinburgh to Inverness would also be increased and journey times would be cut by half an hour, while the main road to the Highlands, the A9, is to be dualled between Inverness and Perth.
The A96 Inverness to Aberdeen road will also be upgraded to dual carriageway between the A9 and Nairn under the government's plan.