Campaigners fighting to improve the A82 Inverness to Glasgow road claim it would take 375 years to match the level of funding that has been committed to upgrading the A9.
Members of a pressure group believe the scenic Highland route has been overlooked while the Scottish Government invests heavily in other “glamour projects”.
The A82 Partnership said, based on current levels of spending, it would take almost 400 years to reach the £3billion committed to dualling the A9 between Perth and Inverness.
However, Transport Scotland last night pointed out that almost £60million has been invested in the A82 over the past seven years.
Frustrated residents were reacting after an announcement from the government agency that the speed limit on three sections of the A82 is being downgraded.
Speed limits will be reduced from the national standard of 60mph to 50mph from Tarbet to Inverarnan, Onich to Fort William and Glen Gloy to Letterfindlay Lodge, a total length of over 25 miles.
The A82 Partnership believes the road is as important to the economy of the West Highlands and Islands as the A9 is to Inverness and beyond.
They also argue the move demonstrates why it is time the road was recognised as part of the national network and brought up to the appropriate standards.
Councillor Brian Murphy, chairman of the A82 Partnership, said: “This is official recognition by Transport Scotland that the A82 does not come up to national network standards.
“It is regrettable that, rather than investing in the A82, they are applying a speed restriction.”
A spokesman for the group added: “With billions of pounds being spent on the glamour projects on the A9, and the A96, it is surely time that the A82 is recognised as part of the national network and brought up to the standards required of such a network.
“Transport Scotland, who have announced that they are spending £3billion on duelling the A9, have spent an average on £8million each year on the A82 during the last decade – at this rate it would take 375 years to spend the same amount on the A82.”
Transport Scotland said the locations along the A82 are generally not representative of a national speed limit, and are being downgraded accordingly.
A spokeswoman said: “The sections have rural alignment, and may include sharp bends, narrow verges, frequent double white line systems, undulating and with low forward visibility.”
On the issue of funding, a spokeswoman said: “We do understand the importance of the A82 to communities in the area and we are in regular discussion with them about our plans for the maintenance of the route with £57million invested since 2007.
“We are taking forward work to improve the route between Tarbet and Inverarnan with ground investigations taking place over the next couple of months to help inform the ongoing work to design a preferred route by next summer.
“Work is also continuing on the £9.2million scheme at Pulpit Rock to remove the bottleneck there and on the construction of the £5million A82 Crianlarich bypass.”