Good question. I am disappointed in the extreme lack of definition and explanation on almost all the graphs in this group.

But baseline means the average daily ridership. Maybe that’s averaged over the years by month, week, day of week or calendar date. But however the baseline is determined, any given day is almost guaranteed to be at least a little different from the baseline. All of the curves start within 20% of baseline. All but one within 10%. That is normal.