The SNP has been accused of “betraying” rural communities after analysis suggested it would take more than a century to upgrade the A9 at the current pace of investment.
The Scottish government promised more than a decade ago to dual the entire 77-mile trunk road between Inverness and Perth, but it has been dogged by delays and rising costs. To date, about 11 miles have been completed.
The Scottish Conservatives said it would take 111 years to complete the project if the average annual expenditure rate since 2012 of £37.9 million continued.
Transport Scotland estimated in 2008 that dualling the A9 would cost £3 billion, but the Tories said the real cost, when adjusted for inflation, stands at £4.67 billion.
Based on spending to date of almost £456 million over 12 calendar years, the party calculated that a further £4.21 billion will be needed to finish the project.
It said it highlighted the “pitiful, snail-paced progress” of a project the SNP originally promised to complete by 2025.
Ministers have angered campaigners by confirming that a parliamentary statement on the renewed timescale for dualling the A9 could still be weeks away, despite having been promised in the autumn.
Graham Simpson, the shadow transport minister, said the SNP-Greens continued to treat communities reliant on the A9 with “contempt” and insisted that the Scottish Conservatives would make dualling it the first pledge of their general election manifesto.
“These figures demonstrate the appalling betrayal by the SNP of those who rely on the A9,” said Mr Simpson. “Every day that these essential upgrades are delayed, more lives are put at risk on this deadly road.”
Transport Scotland insisted that Parliament will be updated on the programme for completing the remaining sections in the coming weeks.
A spokesman also disputed the Tories’ claims, saying: “This is simply not the case. Ministers are committed to dualling the A9 between Perth and Inverness and work is continuing across the route.
“As the then minister for transport confirmed to Parliament in February this year, this decision-making includes consideration of different contractual approaches, such as design and build contracts and public-private partnership contracts, to determine the most suitable procurement options for the remaining sections of the A9 dualling.”
More than 300 people have died on the A9 between Perth and Inverness since 1979. These include 12 fatalities in 2022.
In February, Jenny Gilruth, the then transport secretary, said measures to improve safety on stretches of the A9 had commenced. The work included enhancements to signing and road markings, initially between Birnam and Dalguise and the installation of electronic signs to display safety messages between Perth and Inverness.