Any new work to upgrade the A9 would not start until April 2011 at the earliest, a Highlands MP has claimed.
Dualling the A9 from all the way to Inverness could cost £600m
Lib Dem Danny Alexander said the timescale was revealed in a letter to him from the chief executive of government agency, Transport Scotland.
The MP said this would fall outwith the current Scottish Parliament's term and undermined government pledges that a revamp was a priority.
The Scottish Government said it was committed to making improvements.
The road, the main route to the Highlands, stretches all the way to Caithness but upgrades are likely to be concentrated on the Perth to Inverness section.
Mr Alexander said in his letter, Malcolm Reed said if new stretches of the road were identified in next summer's Strategic Transport Projects Review to be turned into dual carriageway then funding would not be allocated and work started until 2011-2012.
Mr Alexander, MP for Inverness, Nairn, Badenoch and Strathspey, said: "Amidst great fanfare, new SNP ministers led people to believe the A9 would be a high priority for their government.
"It is astonishing that they are now proposing to do nothing within their term of office beyond the positive programme of improvements already planned by the previous government."
Responding, the Scottish Government said it remained committed to improving safety on the route.
A spokeswoman said: "In the short term we are looking at the immediate priorities for investment, and we are absolutely committed to plan for dualling of the A9.
"Options will emerge from the Strategic Transport Projects Review, which is due to report next summer. We will consider these options and take an informed decision on all the evidence including costs and benefits."
In October, a report found dualling the A9 road from Inverness to Perth could generate almost £1bn for the Highlands and Islands economy.
Highlands and Islands Enterprise and transport campaign group Hitrans estimate journey times could be cut by 22 minutes.
The A9 Perth to Inverness Economic Appraisal Study predicted that 724 jobs could be created in the short-term - rising to 4,500 over 30 years.
Previous estimates have put the cost of dualling the stretch at £600m.
The A9 has previously been branded one of the most the deadly roads in Scotland.
More than 80 fatal collisions have occurred there since 2002.