 It marks the boundary between the valleys of the Romanche and the Guisane, a tributary of the Durance which has its source at the col.The valleys are linked by national route 91 (Grenoble – Le Bourg-d'Oisans – Briançon).The Lautaret is one of the lowest points on the ridge line which separates the "north" (mainly in the Rhône-Alpes région) and "south" (mainly in the Provence-Alpes-Côte d'Azur région) geographic areas of the French Alps.