"Upon boarding, Metro staff will announce that each participant should select a seat of their choice. After 2 minutes, you can remain in your current seat, select a new seat, or get off the train and board another train."
Further details check here
You do have to pay for your ride, but the speed dating is free.
* the clip art for this event truly shows Metro might need to think about hiring a graphic designer. I mean why is the Space Shuttle there? I know we have one, but why is it in there?