I take the seabus everyday to work and it's by far my favourite part of the morning. It's also the most ideal mode of public transportation to draw on (in my experience). It doesn't make frequent stops or sudden turns, no one gets on or off for 15 minutes and at the time I take it, there's always plenty of room so I can draw without the constant scrutiny of my fellow commuters. Also, most people are so busy enjoying the view they don't notice me staring while I scribble their likenesses :)
