I note that another contributor has suggested that the B847 that runs west from Calvine could be one of the 'roads to the isles' due to some possible connection to the song once made popular by Andy Stewart which has the line 'and by Tummel and Loch Rannoch and Lochaber' etc. But does a traditional [?] Scottish song give the route any legitimacy, or did it just sound right? If there was a link between the song and a road, then maybe the
B8019 along the north side of Loch Tummel might be a better candidate. But were any of these roads drove roads for cattle? From what I've read it appears that Highland beasts were often driven along 'soft' routes avoiding stony roads which could damage the hooves of cattle, whilst the various routes would probably be heading south towards the trysts at Crieff and Falkirk. I think there's plenty of room for confusion between an old Andy Stewart song and modern tourist blurb that invites travellers to take the A830 west from Fort William to Mallaig as a road to the isles.