The subway has a sound profile uniquely its own. The curves of the tunnel echo back the scrape of steel wheels on the tracks. Brakes squeal as the train slows, arriving at the next station. Another train pulls through, vibrating and rattling as it passes. Inside the car, exterior noises are muffled, overtaken by the sounds of conversation and passengers shuffling quickly on and off the train. On the subway you are free to engage, or just sit quietly with your own thoughts, alone, but not lonely, in a crowd.