Some of the quick life sketches I drew on crowded trains in Tokyo last summer.
I find drawing on busy commuter trains exhilarating. You never know whether your view is going to be blocked as the carriage fills with people, or whether the subject is going to shift position, get off at the next stop, or notice they're being drawn and feel uncomfortable. The trick is not to draw the person in front of you but one sitting further down the carriage. You draw rapidly and surreptitiously from sideways glances, getting as much information down, as quickly as you can.
Dozing passengers are a safe option!
Often the resulting pen line can have a nervous energy that might be hard to achieve in more considered drawings, the white spaces have a natural compositional dynamism . I'm often surprised by the results.
I tend to draw more on Japanese trains than those in the UK, crowded trains with standing passengers offer unusual angles and it's easier on the Japanese networks because all the seats are against the carriage walls facing each other. London tube trains have similar layouts but more cramped so I find them a little too intimate for sketching passengers.
Tomorrow I'm off on a 2 hour train journey though, so if I get any drawing done I'll post when I get back!