The controversial £500m project to extend the M74 in Glasgow will be delayed by up to a year because of legal action by opponents.
The stretch of road will link the M74 and the M8
Ministers decided in March to press ahead with the scheme, despite a public inquiry which recommended that it should not proceed.
Friends of the Earth Scotland and Joint Action Against the M74 (Jam74) lodged an appeal against the decision.
It has emerged that work is now unlikely to start until June 2007.
The project is expected to take about two-and-a-half years to complete.
It had originally been envisaged that the link would be finished by the end of 2008.
The new road would follow a route from the Fullarton Road Junction near Carmyle to the M8 just west of the Kingston Bridge.
In March the executive said it was planning to go ahead with the project - despite the recommendation of a public inquiry reporter.
Last month those campaigning against the link lodged papers with the Court of Session in Edinburgh.
Opponents claim the scheme will create more traffic and pollution and say the executive has failed to give adequate reasons why it disagreed with the inquiry's conclusions.
Friends of the Earth Scotland's chief executive, Duncan McLaren, said it wanted the court case to be dealt with as quickly as possible.
"The communities affected by this massive scheme have already suffered blight as a result of this motorway proposal for far too many years," he said.
"The best way for the executive to end that blight would be to drop the proposal for good.
"What we are attempting to do is prevent £500m of taxpayers' money from being wasted on yet another pointless and environmentally-damaging motorway project."
The executive believes the extension will create 12,000 jobs, reduce congestion and cut road traffic injuries by up to 50 a year.
The road project has the support of business leaders and motoring organisations.