I guess in the 1950is or a bit later. See the skis at the back.
PostAuto Schweiz in Swiss Standard German, Now Postbus. CarPostal Suisse in Swiss French, and AutoPostale Svizzera in Swiss Italian) is a subsidiary company of the Swiss Post, which provides regional and rural bus services throughout Switzerland, and also in France and Liechtenstein. In Swiss German dialect they are also called Poschi or Poschti.
The Swiss Post Auto service evolved as a motorized successor to the stagecoaches that previously carried passengers and mail in Switzerland, with the Swiss postal service providing postbus services carrying both passengers and mail. The buses operated by PostBus are a Swiss icon, with a distinctive yellow livery and three-tone horn. The company uses an image of a posthorn as a logo on its buses and elsewhere. On some mountain roads, indicated by a traffic sign of a yellow posthorn on a blue background, the buses have priority over other traffic.
Lenzerheide, Heidsee, 1920
1849: Creation of the postal network diligence.
1906: First service of PostBus between Bern and Detligen.
1919: Inauguration of the line crossing the Simplon Pass.
1921: Grimsel Pass, Furka Pass, San Bernardino Pass and Oberalp Pass are open to traffic.
1923: A three-tone horn is installed on the buses travelling on mountain routes.
1949: The bus lines of the Principality of Liechtenstein are operated by PostBus.
1959: All buses are of the same yellow color.
1961: Last service of horse diligence on the line Avers-Juf*.
2003: For the first time, PostBus carried more than 100 million passengers.
2005: PostBus Switzerland established as a subsidiary company of Swiss Post.
Juf 2126 m or 6975 ft above sea level
Juf is a village in the municipality of Avers in the canton of Graubünden, Switzerland. At 2,126 metres (6,975 ft) above sea level, it is the highest village with permanent residents in Switzerland and in Europe. Juf has a population of about 24 inhabitants divided over 6 families in a concentrated settlement. They were 20 in 1991 and 30 in 2001. The first inhabitants were immigrant Walser who arrived in 1292.
The first Post Auto Chur-Tschiertschen 1925, transporting Mail and people;
1951, with a slide back roof.
The posthorn, children sang perhaps still do, tutato Postch isch do...or tutao Poscht Auto...♫