You know those rumble strips they put in the road surface to alert inattentive drivers of a potential danger? The audible rumbling it produces is a boring “Brrrrrrrr.” Invent a machine that puts down “musical rumble strips” by varying the distance between the strips. When driving over them, for example, you might hear the Shave and a Haircut riff.
Roads like that exist, even if none of the examples play “Shave and a Haircut” and there’s not a machine to make it.