Close harmony honking

Car horns produce a range of tones which vary from vehicle to vehicle. Within limits, the tone can be varied.

Many modern vehicles have wireless connectivity which allows them to communicate with other vehicles in their vicinity. A simple software upgrade would allow cars in close proximity to share information about what tones they can emit.

Therefore, when a group of cars with a useful tonal range are fortuitously gathered together, they could play music by honking their horns in sequence.

Tunes would most likely be limited to "Twinkle, twinkle little star" in traffic jams and small car parks, but at large supermarkets J.S.Bach's "Tocatta and Fugue in D" or Saint-Saëns' Third ("Organ") Symphony might well be possible.