by Thomas Telford in the 19th. The modern route is based on that designed by Telford, but with a number of improvements primarily dating from the 1920s and 30s. These include a diversion across Rannoch Moor, and another around Loch Leven which was subsequently replaced by the Ballachulish Bridge.

Several travel guides have praised individual parts of the road, such as the section from Tyndrum to Glencoe