From Edinburgh, the A90 travels west and connects to the M90 motorwaybypass route that leads to the M9: however, it is only possible to travel northbound when reaching this connection. 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, the M90 again becomes the A90, now running north east to Dundee and through the Kingsway road system. It then passes Forfar, Brechin and Stracathro. After crossing the Cowie Water just north of Stonehaven, a new junction takes the A90 road north as part of the Aberdeen Western Peripheral Route, rejoining the A90 at the village of Blackdog where the AWPR terminates. Proceeding north, the route crosses the Ythan Estuary near Ellon, skirting Peterhead on its way to Fraserburgh. The A952 road via Mintlaw serves as a more direct inland bypass to the A90 road in its northerly extent. The Dundee to Aberdeen stretch of the A90 is notorious for speed cameras. Previously, the trip from Dundee to Aberdeen along the A90 entailed over a dozen speed cameras including a majority of fixed Gatso types as well as locations used by mobile camera vans. These cameras were found on long fast stretches of road, and shortly before dangerous junctions, such as at the Laurencekirk junction where a speed limit is in force. This was introduced due to this junction's appalling safety record. A similar speed restrictionwas imposed at Forfar until two new grade-separated junctions were built, after which the restriction was lifted. In 2017 Average Speed Cameras were erected between Dundee and Stonehaven, with 15 per side, spaced approximately every 5 miles for a total of 30 cameras. BBC News reported in January 2018 that speed limit compliance had increased from 2 in 5 to 99 in 100 drivers. The A90 was extended considerably on 30 March 1994 so as to give a continuous route number from Edinburgh to Aberdeen, since the A90 originally stopped at Inverkeithing. The former A85 went from Perth to Dundee; the A929 Kingsway through Dundee and then towards Forfar; the A94 from Forfar to Stonehaven; and the A92 from Stonehaven to Fraserburgh. The A92 did not go to Peterhead. The evidence of the numbering change can still be seen on the older road signs along the route where the original route numbers have been covered over with "A90" plates. The section of the A90 between Balmedie and Tipperty was upgraded to dual carriageway in 2018. A short stretch of the A90, from the southern terminus of the M90 to Barnton Junction, is part of EurorouteE15, which runs from Inverness to Algeciras in Spain. The E15 continues northwards on the M90, and southwards on the A902 leading to the Edinburgh City Bypass. The A90 ran along the coast and through Aberdeen until the city was bypassed with the opening of the Aberdeen Western Peripheral Route in 2018. The former stretch of A90 from Stonehaven through to just north of Aberdeen is now part of the A92.
Future
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.
River crossings
A90 bridges span numerous rivers, estuaries and burns including:
