This is a music video about the ridership of Chicago buses and New York subways for the past few years.
Each musical beat is a day, as is each vertical line. One musical instrument represents the daily ridership of Chicago buses, and the other represents the daily ridership of New York subways. (Both are measured at fare collection points.)
The vertical line on the graph also represents the daily ridership. It is colored according to the city whose ridership was proportionately higher for that day. The top of the line is the rate for the city with proportionately higher ridership, and the bottom of the line is for the one with proportionately lower ridership.
Daily ridership is also represented by the white/grey ticks at the left and right of the video. The brightest tick is for the present day, and the duller ticks are for progressively earlier days going back seven days.