Representing a significant component of the country's transport infrastructure, the M90 Motorway links South Queensferry with Perth in E Central Scotland. It represents the most northerly of Britain's motorways, extending for 30½ miles (49 km) to Craigend Interchange, 2½ miles (3.5 km) south of Perth. The M90 then splits into two branches; one extends for a further 3 miles / 5 km to Broxden Junction to the west of Perth, where it joins the A9, while the other continues for 2 miles / 3 km over the Friarton Bridge to link with the A90 that proceeds onwards to Dundee.
Broadly the motorway opened in sections from south to north between 1964 and 1980. The first section lay immediately to the north of the Forth Road Bridge and opened with that structure in 1964, extending as far as Fordell, and including the A823(M) spur into Dunfermline. The engineers were Mott, Hay & Anderson working in partnership with Fife County Council, while the contractors were Whatlings and the total cost £1.4 million. An abandoned 250-m / 820-foot section at Fordell, which was once the end of the original motorway, remains extant. The next section was the Crossgates - Kelty - Cowdenbeath bypass which opened in 1969, designed by W. A. Fairhurst and Fife County Council, and executed by Tarmac Construction. This work was expensive at £4.6 million because considerable groundworks were required to mitigate the risk of subsidence caused by old coal workings. Three years later, in 1972, came the Kinross - Milnathort bypass, designed by Babtie, Shaw & Morton and constructed in two years by Fitzpatrick & Son at a cost of £5.7 million. This was the first section of a British motorway to be built with a concrete surface. Rumour suggested that this surface was designed so the road could be used as an emergency runway by the air-force should RAF Leuchars have been destroyed if the Cold War warmed up.
The next section climbs the relatively shallow southern slopes of the Ochil Hills, connecting Arlary with Arngask by Glenfarg. Designed by Babtie, Shaw & Morton and built by Whatlings, work began in 1974 and was completed three years later at a cost of £5.1 million. 1977 also saw the completion of the section between Muirmont Interchange and Moncreiffe Hill, 4½ miles 7 km to the north, which included the crossing of the River Earn. This section cost £10.1 million and was also by Babtie, Shaw & Morton and Whatlings. The following year the entire northern section was completed, including Craigend Interchange, the approaches to Friarton Bridge, and the Perth Bypass to Broxden, at a total cost of £18.8 million. The Perth Bypass was designed by Tayside Regional Council and built by contractor William Tawse. The missing link between Glenfarg and Muirmont Interchange took a further two years, again designed by Babtie, Shaw & Morton and built by Tarmac Construction at a cost of £8.2 million. This was a significant challenge, bringing the motorway down the steep northern slopes of the Ochils - a drop of around 125m / 410 feet - which involves the tightest turn to be found in the British motorway network as the road turns through 130°. The combination of the turn and descent means heavy goods vehicles are advised to select a low gear and the unwary often brake continuously.
Around Glenfarg and to the south of Bridge of Earn, the motorway follows the route of the former Inverkeithing and Perth Section of the North British Railway. Despite surviving the Beeching cuts of the 1960s, this railway closed in 1970. The closure was controversial because it represented the most direct route from Edinburgh to Perth and this decision featured in a public inquiry in 1971 which was called to consider the route of the motorway.
Landmarks along the route include the Forth bridges, the immense Amazon fulfilment warehouse at Dunfermline, Benarty Hill, Loch Leven, Balmanno Castle and the Friarton Bridge.
