More people in a single apartment will definitely increase spread. I'm not sure small apartments per se make any difference unless the ventilation is interconn

More people in a single apartment will definitely increase spread. I'm not sure small apartments per se make any difference unless the ventilation is interconnected. I'm not sure how common that is. I agree that everything is more crowded in NYC, but the only thing I can think of more crowded than a subway car is a nightclub. Estimating from ridership numbers, the average New Yorker rides the subway 15-30 minutes per day. The ceilings aren't even that high, just the number of people per unit volume is incredible. One of the case studies I saw showed it spreading on a long distance bus between people sitting four rows away from each other.