The A9 between Perth and Inverness must be upgraded to a dual carriageway to reduce the "atrocious" number of accidents, according to an MSP.
The A9 road has been described as Scotland's deadliest
Perthshire MSP John Swinney said the route was one of the most deadly in Scotland with 82 deaths in the last five years.
The former SNP leader said the road was "fundamentally unsafe".
The transport minister said the £600m for a full upgrade was not available and that promise had not been made.
Speaking on BBC Radio's Good Morning Scotland programme, Mr Swinney said: "The government has promised to undertake junction improvements and promised this in 2002.
"It promised to have the work finished by the spring of this year and there is not a single piece of construction at this junction started.
"When we get information that this is the deadliest road in Scotland, we need urgent action from the government."
Mr Swinney said the change from single road to dual carriageway along the route created "a climate of confusion".
Transport Minister Tavish Scott said he was frustrated that a planned upgrade of the Ballinluig junction had not been completed.
The Scottish Executive has said improvement work on the junction at Ballinluig, near Aberfeldy had been delayed due to poor ground conditions.
Mr Scott conceded the A9 had bad road traffic statistics and said ministers were aware of the public's safety concerns.
He added: "We will make sure construction work starts on the Ballinluig next year.
"I entirely appreciate the frustrations about that particular junction. But it's also about how we drive on the road."
The minister said he was "very, very disappointed" that engineering constraints had contributed to the upgrade delay.
"I am fed up with it too and want it sorted."
On the issue of a full upgrade, he said: "We don't have the money for that right now. No government has said it would spend the £600m to dual the entire length of the A9, which is what's being called for.
"I think it's important to get the balance right between improved safety, better signage and making sure we do solve the issues that have rightly been raised."
The executive said it did not have the funds to upgrade the A9
Mr Scott said ministers were keen to encourage more commuters to travel to Perth by train rather than car.
He added that other roads in Scotland carried more traffic than the A9 and people would say they, too, needed to be upgraded.
Sue Nicholson, of the RAC Foundation, said motorists could become too easily frustrated on the main road north.
"The biggest problem is probably where it goes from single carriageway to dual carriageway," she said.
"People become extremely impatient when they get stuck behind a queue of traffic and they try to pass and overtake in inappropriate places and that's often the cause of problems ."