Courier service Hundreds of Postbuses simultaneously honk "Dü-Da-Do" to mark the Horn anniversary

Hundreds of Postbuses in mountain regions throughout Switzerland sounded their three-tone horn ("Dü-Da-Do") simultaneously on Wednesday morning. The drivers were celebrating the post horn, which is 100 years old this year.

Between 9.55 and 10.00 a.m., the Postbuses sounded their horns for around 30 seconds each. Up to 700 Postbuses took part in the "Dreiklang im Einklang" campaign, PostBus announced.

Of the 2,300 Postbuses in Switzerland, a good 700 are equipped with the tri-tone horn in addition to the standard horn. Graubünden has the densest post horn network, followed by Valais and Ticino.

The tri-tone horn was introduced in Postbuses 100 years ago for safety reasons. Today, the horn is sounded according to regulations and never in built-up areas. The use of the 120 decibel post horn is limited to "mountain post roads". The catchy triad of the post horn comes from the overture to the opera "William Tell" by Italian composer Gioachino Rossini.