Play both as quietly and as near to unison with those around you as possible.
Gather any number of cars in a suitably large space. For the duration of the piece, beginning with a single horn, each driver should honk their horn in long plateus of sound, so as to generate an overlapping and continuous medium. The cars’ engines should be off, unless moving to another location in the space. Open duration.
Take the sand in your hands or some other vessel and let it slip through your grasp. Let it go in torrents or trickles. Let it fall from a height or from very near to the ground. Let it fall on planes and inclines; inside, outside, and onto objects; into piles and drifts and empty spaces.
When the train door closes and as the train begins to accelerate, open and sustain a long tone. Your sound should be soft but present. As the next train arrives and its doors open, conclude your tone. Repeat.