The full design of the dualled A9 will be unveiled by the start of next year.
Infrastructure Secretary Keith Brown told the Scottish Parliament that the upgrade of the major road was on course to be completed by 2025.
He said a quarter of the preferred route had already been announced, with the remainder to be confirmed by “early 2017”.
Some MSPs, including Highland member Mary Scanlon, have raised concerns work to dual the trunk road is taking too long – but Mr Brown insisted it was “progressing well”.
He said: “Construction of the A9 dualling began between Kincraig to Dalraddy in September 2015. The first section is expected to be completed by the summer of next year.
“The remaining dualling is on course to meet the Scottish Government’s target of being completed by 2025.
“The design of remaining projects is progressing well, with one quarter of the preferred routes announced last week and the rest anticipated during 2016 and into early 2017.
“Exhibitions are currently taking place at which the route options are being displayed to the public for comment.”
Mr Brown also said that a dualled A9 would bring tremendous benefits to the Highland economy.
The road is currently covered by controversial average-speed cameras.
But, responding to a question from fellow SNP MSP Mike Mackenzie, Mr Brown said: “Mr MacKenzie is absolutely right that the construction will have benefits for employment and that dualling will have longer-term benefits in relation to increased productivity and a more efficient transport system.
“The A9 plays a vital role in supporting the economy not just of the Highlands and Islands but of Scotland, with an estimated £19billion worth of goods being transported annually on it.
“The journey time and reliability benefits that are associated with the dualling programme will reduce transport costs for businesses.
“The upgrading of the road itself will also reduce driver stress and frustration and lead to improved safety for the 12 million vehicles per year that travel between Perth and Inverness.”
About 80 miles of single carriageway between Perth and Inverness are to be made into dual carriageway by 2025.
The Scottish Government has said it expects about half of that work to be completed by 2022.