From Figure 1, we can clearly tell that the number of Citi Bike users in March 2015 generally decreases across the week, with a sharp decline on Saturdays before increasing again on Sundays. While we can also tell that the number of customers using the bicycles are relatively constant across the week, only increasing on Sundays.
In comparison, for December 2016, we can see that there's a bit more fluctuation between the riders through the week but we still see that sharp decline on Saturdays.
We also generated an additional plot with statistical errors for the trip counts using the Poisson statistics (Figure 3).