When I lived in the Washington, DC suburbs from 2017 to 2021, I rode the trains many times, to work, to museums, to concerts and more. The quickly-rotating cast of characters on the trains made up one of the best portrait studios I ever had access to.
I think Walt Whitman would have loved the Metro. What a place to revel in the beauty, the variety, the dignity of just plain people in their idle moments, with their guard down. I can imagine him beaming, scribbling away.