I just have to ask the OP...since one of the inspirations for this interactive's elegant design is Edward Tufte, did you take inspiration from his version of Harper's annotated hospital bill? Because that was the first thing I thought of when seeing the beautifully-done annotations alongside the dense subway arrival time data.
The chart I'm talking about is in Tufte's Envisioning Information, and is one of my favorite examples in all of his books: https://pbs.twimg.com/media/BpxpK-1CIAAl2yH.png:large