The A90 is the historic route north from Edinburgh to Perth, Dundee and Aberdeen - crossing the Firths of Forth and Tay.
There has, since 1990, been a considerable renumbering of A-class roads leading to the northeast of Scotland. The original A90 only ran between Edinburgh and Perth. In the mid-1990s, the number was extended northwards as far as Aberdeen, taking over stretches of A85 (Perth-Dundee), A929 (Dundee-Forfar), A94 (Forfar-Stonehaven), and A92 (Stonehaven-Aberdeen).
Historically, the route began at Edinburgh's old West Port, some 750m further to the southeast and now the Grassmarket area. While the first part the road survives as Kings Stables Road, Lothian Road, linking Edinburgh's 1766 New Town to the old Linlithgow and Glasgow roads has obscured the northern section. Traces remain in that the Caledonian Hotel and Rutland Hotels are both set back at an angle from the modern road.
The A90 now begins at Edinburgh's West End, a seven-way junction considerably simplified through the use of restricted turnings. The original A90 started directly along Queensferry Street, but this is now closed off, forcing a diversion through Charlotte Square first. The only access is from the A8 eastbound or the A702 northbound. (The direct route may be reopened as part of new traffic management plans for central Edinburgh.)
Charlotte Square is the peak of architectural elegance in Edinburgh's First New Town. The building plots were fued with strict conditions on building style and use, and all the buildings in the square are original. The whole south side of the square is now owned by the National Trust for Scotland, and used as their national headquarters as well as a shop, cafe and restaurant. The north side of the square includes two properties of note, the Georgian House (NTS, open to the public), and Bute House, the official residence of the Secretary of State for Scotland, and now used as the location for meetings of the Scottish cabinet.
For many years, traffic in Charlotte Square was a large one-way system, but now the south and east sides are both two-way and the north and west sides have restricted access (from the SW corner).
After leaving Charlotte Square, the A90 returns to the junction at the West End, and turns into Queensferry Street, through Edinburgh's Second New Town. This
The next notable feature along the road is the high Dean Bridge and, just upstream, Dean Village. The bridge was built speculatively to open up development ground on the north side of the Dean Water.
The Forth Road Bridge, opened in 1964, was one of the wonders of the age, the longest bridge span in Europe at the time, and the third longest in the world.
The bridge works started at the Crammond Bridge in Edinburgh
The old Kirkliston-Queensferry Road was diverted to a new interchange at Echline, and later reclassified as the A8000. Initially it was a B-class road, but the M8 and M9 works at Newbridge gave it increased importance. Today, it's one of the most imporant road links in the area, but is still not a Trunk Road and renewal is limited by local government spending.
The A90 bridge is the Forth Road Bridge, but half a mile downstream is the original Forth Bridge - completed in 1890. Over a century later, it's still the world's longest pure cantilever bridge.
Iain Banks' novel The Bridge is based around the Forth Bridges.
The main attraction in North Queensferry is Deep Sea World,
The Forth Bridge North Approach Road joined the old A90 at Fordell, north of Inverkeithing.
Some planning maps show a roundabout at the junction, but there's no trace of this on the ground. It looks like a simple staggered junction. The stub of the motorway is still used as a materials store for the Council roads department.
The original line of the M90 was the spur to the A9, west of Perth, with the Friarton Bridge being opened as the M85, leading onto the A85 through to Dundee. With renumbering of the A85 as A90, the Friarton Bridge was reclassified as a continuation of the M90. However, the M90 spur to the A9 remains as part of the M90, and is the longest motorway spur in the United Kingdom without it's own number.
The A90 between Perth and Dundee was, for many years, one of the most dangerous roads in Scotland.