 Construction started in the US-occupied zone of Salzburg and Upper Austria, partly relying on the pre-war planning, and were extended after the country gained full sovereignty by the 1955 Austrian State Treaty.The first section of the West Autobahn up to Mondsee was opened in 1958, by 1967 the route between Salzburg and Wien / Vienna was completed.From 1959 onwards the Süd Autobahn was built to reach the southern state capitals of Graz and Klagenfurt from Wien / Vienna.