This is what it looks like when hundreds of thousands of people stand still at the exact same time.
The Washington Metropolitan Area Transit Authority ran rush hour-level train service for 17 straight hours on Monday to get revelers (and the odd dissenter) in and out of downtown D.C. for Barack Obama's second inauguration. By the agency's preliminary tally, 800,000 passengers moved through the Metrorail system that day, from 4 a.m. Monday through 2 a.m. early the next morning. And that total doesn't count public bus passengers or the swarms of people who came to town in charter buses.
The agency's planning blog has since posted this remarkable graph of the day's ridership:
Washington Metropolitan Area Transit Authority
That deep trough right at 11:30 a.m.? That's precisely when the inauguration ceremony was getting underway. This graph perfectly captures what you would have seen on the ground in Washington's metro system (or really anywhere in the city) on Monday: mad chaos throughout the day, with a collective pause mid-morning as hundreds of thousands of people stood still just long enough to listen to the president (and what they thought was Beyoncé). For those moments, there were fewer people riding the metro system than there were using it before dawn Monday morning.
This pattern of inauguration-goers appears particularly clearly because Monday was also a federal holiday in the capital, with significantly fewer people commuting to work during regular rush hours. On a typical weekday, the system has recently been averaging about 723,000 trips a day, although that figure is hard to compare to Monday given the holiday. Over the course of a single day, this is the pattern of what ridership more typically looks like during holidays and average weekdays (note that the y-axis measures rail entries per half-hour, not quarter-hour):
Back in 2009, Metro set a ridership record for Obama's first swearing-in. Then, there were about 1.1 million trips taken on the metro system. For a little further historical context: Monday's Metrorail ridership was still not as high as it was during high-profile visits to the capital over the past two years by the Dalai Lama and... Jon Stewart.