The First Minister said finance models were currently being examined for the preferred solution for the A83 Rest and Be Thankful in Argyll – estimated to cost up to £470million – which has been regularly closed by falling rocks in recent years.
Work to improve the Old Military Road, which is used as a diversion route, is also planned to begin this year, ministers have said.
The pledge was made as the Scottish Government held a public meeting in Inveraray, as part of a Travelling Cabinet programme which sees ministers visit different areas the country. It was the first to take place since it was halted by the Covid pandemic.
The plans for the Rest and Be Thankful tunnel were unveiled in June by Transport Scotland.
But ministers were asked – given a recent report which highlighted challenges around funding of infrastructure projects – if money would be found for the project in “this parliament or the next”.
Yousaf replied: “There is an absolutely a firm commitment to the preferred option around the A83, to the credit of Argyll and Bute Council it was the very first issue they raised with us when they had a meeting earlier on today, they asked that very question, does the commitment mean funding.
“The answer to that is yes. There’s no point in making a commitment in spirit without the money, the money has got to be there.
“The funding position is very difficult around infrastructure, the Finance Secretary is looking at finance models at the moment to see how we progress those funding options.”
Transport Secretary Mairi McAllan referenced a groan from the audience at the beginning of the meeting when the Rest and Be Thankful was mentioned, saying it was “understandable”.
She said: “I was at the Rest and Be Thankful this morning with Transport Scotland officials and they were talking me through, I had the visual right in front of us, on the work that is due to be taken. The First Minister has perfectly clearly outlined our financial commitment to that, and that is something I will keep taking forward.
“My reflections so far, having been in the post, is my priority is a permanent solution as soon as possible and reassurance on safety in the meantime.”
She said it was hoped work would begin on the Old Military Road this year, with instruction already given to Transport Scotland officials to progress it.
A wide variety of questions were put to ministers during the discussion at the Inveraray Inn, ranging from accusations of “selling out” on independence, the tourism tax, legislation on short-term lets, fuel poverty, the fishing industry and plans to close the primary school on the Isle of Luing.
Ministers were also asked to join in congratulating golfer Bob MacIntyre, from Oban, who helped Europe lift the Ryder Cup at the weekend.
The cabinet had also met at Inveraray Parish Church before hosting the public discussion to hear about local issues.
And ahead of the meeting, Yousaf met with a community group to see their ongoing work in regenerating the local pier.
The group Inspire Inveraray purchased the pier in July 2023, with just over £120,000 from the Scottish Land Fund with the aim of bringing it back into operation. It had previously been privately owned for 20 years and closed to the public for the past five years.
Yousaf said: “Community empowerment is a key aim for this government and it was great to see in person a perfect example of a local group, supported by the Scottish Government, taking power of local assets for their community benefit as well as supporting the local economy.”