Bulb Horn for Hire
One of the most famous pieces for car horns was written by Gershwin, where he asks the percussion section to play four distinct pitches (A,B,C & D) in time to the music. This is surprisingly difficult and calls for a percussionist who can squeeze balls hard and fast. Mainly, however, car or taxi horns are used within orchestral music. There are UK specialists that have several octaves of taxi horns for educational demonstrations and films. Bill Bailey famously uses bulb horns during some of his live performances. They're funny and you should watch them.
Gershwin - An American in Paris
Italian - Clacson
French - Klaxon
German - Autohupe