A campaigner said the A9 had been treated like a forgotten back road
Civil engineers said they knew for years a target to dual the A9 from Inverness to Perth by 2025 would not be met.
The Scottish government committed to the date in 2011, when the project was predicted to cost £3bn.
In February this year, the then transport minister Jenny Gilruth said the target was “unachievable”.
She said the project had been hit by delays caused by the Covid pandemic, Brexit and the war in Ukraine.
Eleven miles (18km) have been dualled in 10 years, leaving about 77 miles (124km) of road to still be upgraded.
MSPs are due to hear from Civil Engineering Contractors Association (CECA) Scotland as part of their consideration of a petition calling for details of the revised timetable for the project.
The industry body said the dualling so far had been “glacial” and engineers had long known the project was progressing too slowly to be completed on time.
Grahame Barn will give evidence on the A9 to Holyrood’s petition committee
Speaking ahead of Wednesday’s meeting, chief executive Grahame Barn told BBC Scotland: “We have known for a number of years that the pace at which the design and road orders were coming forward meant it was impossible to achieve 2025 by that time.”
Campaigner Laura Hansler, who lives in Kincraig, near Aviemore, is also due to give evidence to MSPs on Holyrood’s petitions committee.
She said the A9 had been treated like a forgotten back road, rather than the “spine of Scotland” linking central parts of the country with the Highlands.
Ms Hansler said: “We need focus and we need to stop people getting killed on our roads.”
SNP MSP and former transport minister Keith Brown told BBC Scotland the road project was facing huge challenges.
He said: “It is true across the UK more than other countries that infrastructure projects have been extremely expensive and we have a narrower base of construction companies involved in this work.
“It seems to me, knowing what I know about it, the terms of the project which were taken forward have changed and that is bound to have had an effect.”
