Earlier this year I started to portrait people in the Berlin public transport. I am spending more than an hour every day in the trains so with drawing people I can use the waiting time in a meaningful way while practicing my portrait skills.
I try not to disturb people. I draw them mostly when they are distracted. And no, I do not ask before I do the portraits for one reason: The people would not behave the same anymore. I think there is a big difference to photography. I would not take pictures of people and put them online without asking because these are a 100% accurate. But important to know is that my accuracy is very low. Very often I modify the drawing in a way so that the original person could not be recognized in any way. Sometimes that makes the drawing also more interesting or the person leaves the train and I need to improvise the rest.
The drawings are very small. About 4 cm. I draw them with a mechanical pencil.
Here are some close-ups: