The M90 is a motorway in Scotland. It runs from junction 1a of the M9, south of the Queensferry Crossing, to Perth, passing Dunfermline and Kinross on the way. It is the most northerly motorway in the United Kingdom, the northernmost point being a spur into the western suburbs of Perth at Broxden. A small part of the M90 was originally numbered as the M85 motorway.
History
The first section of the M90 opened in 1964 to coincide with the opening of the Forth Road Bridge and Masterton junction. The next section, the Crossgates – Kelty and Cowdenbeath Bypass, opened on 1 December 1969, with another stretch, the Kinross and Milnathort Bypass, opening in May 1972. The following two sections were due to begin construction around 1973/74, but were put on hold because of the oil crisis. The section from Arlary to Arngask was opened in March 1977; Arngask to Muirmont opened in August 1980, connecting with the completed Friarton Bridge and Perth Bypass to Broxden. As part of the Queensferry Crossing scheme, the M90 was extended southwards across the Firth of Forth over a new cable-stayed bridge in 2017. A short stretch of A90 dual carriageway connects the two parts of M90 - the short M90 section from the M9 and the much longer M90 section that crosses the Queensferry Crossing and extends north to the outskirts of Perth. This short length of A90 dual carriageway was required at this point as Motorway regulations would have prevented certain classes of traffic from using this section of road.
Details
The M90 leaves the east-west M9 in the vicinity of Kirkliston and heads north. The motorway is interrupted by a short stretch of A90 from where the A90 from Edinburgh joins the M90. The road continues as the A90 until it reaches the junction to the south of the Queensferry Crossing - the A90 becomes the M90 again at that point. The crossing opened as part of the motorway on 30 August 2017; the bridge is configured as a D2M and has a speed limit of 70 mph. Previously, the M90's most substantial engineering feature was the Friarton Bridge in Perth, a tall concrete pillared structure which traverses the River Tay. The bridge carries eastbound traffic from Broxden towards Dundee and along the Firth of Tay. The road constitutes most of the southerly part of the A90 corridor from Edinburgh, through Perth, Dundee and Aberdeen to Peterhead along Scotland's North Sea coast. A large part of the northern section of the motorway follows the route of the former main railway line between Perth and Edinburgh via Glenfarg, Kinross and the Forth Bridge, which was closed in 1970 despite this not being recommended by the Beeching report. It is not obvious when first driving along the road but close inspection of the 1:25,000 scale Ordnance Survey maps of the route illustrates this. Another unusual feature of the M90 is that the Kinross and Milnathort Bypass, the section of the M90 between Fruix and Arlary, was the first motorway in Britain to be constructed using unreinforced concrete pavements. Both the south-bound & north-bound Carriageways have since been overlaid by tarmac. The use of Unreinforced Concrete Paving on Carriageways in Scotland is now very rare. Near to its northern terminus, the motorway splits into two branches. The construction of this three-way interchange required the removal of about 900,000 cubic metres of material, mostly rock. The motorway bends through more than 90 degrees, on a compound curve partly of 520.8 m and partly of 694.5 m radius. One branch heads in a north-easterly direction, flowing into the A90 at its end, numbered junction 11. The other branch forms part of the western bypass of Perth, and meets the A9 at its end, numbered junction 12. The gradient is 4.57% uphill and 5.65% downhill on this section. The slip roads forming this branch merge with shared priority to allow HGVs to maintain momentum on the steep upgrade. The Broxden to Muirmont slip road at the centre of the interchange has a radius of 136.4 m, necessitating maximum superelevation of 7%. The M90 forms part of the EurorouteE15 which runs from Inverness to Algeciras, but which is not signposted within the UK.
Issues
The M90 lacks hard shoulders for an section. In this section there are emergency lay-bys at intervals instead. The M90 here has another of the tightest corners on the UK motorway network, for which some traffic can be forced to slow down. The corner cuts through the northern side of the Ochil Hills and has a curve radius of 694.5 m. This corner also coincides with one of the steepest sections of the motorway, for which north-bound heavy goods vehicles are sign-posted to stay in a low gear and often brake continuously through the turn. South-bound HGVs are normally substantially reduced in speed as they make the incline.
