[2] In recognition of this, in 1979, the British government announced that it was giving priority to the upgrading of the route to dual carriageway standard.

After connecting with the M90, it runs as a short section of A-road before turning into the M90 properly at the Queensferry Crossing.

At Perth, beneath Kinnoull Hill, the M90 again becomes the A90, now running north east to Dundee and through the Kingsway road system.

After crossing the Cowie Water just north of Stonehaven, a new junction, opened in 2019, reroutes the A90 road north as part of the Aberdeen Western Peripheral Route (AWPR), bypassing the city to its west past the suburban developments of Peterculter, Milltimber, Westhill and Kingswells, turning east past Aberdeen Airport and Dyce.

In January 2016 the Scottish Government announced £24 million for the design and construction of a new grade-separated junction at Laurencekirk on the A90.

[11] Ground investigations were carried out in 2019 in preparation for upgrading the flat junction between the A90 and the A937 to a flyover after a number of deaths.

[14] However, supplementary draft Orders and an Environmental Impact Assessment Report (Addendum) was published in December 2024 to facilitate the necessary works required at Oatyhill to allow the flyover to be built.

[15] While the Balmedie to Tipperty segment was eventually dualled as part of wider AWPR works, in 2023 the Scottish Government said it had no plans to dual the route north of Ellon.