[catlas3r]

Actually, no they don't. There are 5.6m rides per day. The average trip contains at least two rides: there, and back again. Many trips contain substantially more than two legs, and many people take more than one trip per day.

I can't tell you how many people ride the subway every day, but it's certainly less than half of the number of rides per day.

[throwaway3563]

Number of rides is actually more relevant in this context than number of distinct riders. Each trip involves a new set of people next to you in the train car and a new chance of getting infected.

[catlas3r]

The number of rides is useless in estimating the percentage of the population with high risk for exposure if you don't also have the proportion of the population exposed to that risk.