Metrics for Rallies

From the Post's Dr. Gridlock blog, discussing Metro's problems on Saturday:

"They were figuring on a crowd about the size of the one for the Glenn Beck rally on Aug. 28. That day, about 200,000 more trips were taken on Metrorail than on a typical summer Saturday."

"To say Metro was overwhelmed, that would be more like it. That was no where near enough equipment or personnel to help the people who showed up. Metrorail wound up providing about 475,000 more trips than on a typical Saturday. "

 I've been frustrated by the crowd estimating that goes on for the various events on the Mall.  It's always seemed to me that Metro ridership is a solid indicator with which to compare rallies.  Granted the attendance at different events will make more or less use of Metro and may or may not deter people from using it for their normal weekend activities.  But still the ridership is a solid number, not dependent on aerial photography and the prejudices of the counter.