Metro is celebrating National Dump the Pump Day, which is this Thursday, June 19, by giving away one $100 SmartTrip card to the lucky person who can guess how many people will use the Metrorail system that day.

If you’ve got a guess, you can submit your number on Metro’s web site. Entries must be submitted before midnight on June 19. They’ve got a a handy chart posted if you’re completely in the dark with Metro’s typical ridership numbers. Some other things to keep in mind when making your estimate: the Nationals are not at home on Thursday, and the SILVERDOCS AFI/Discovery Channel Documentary Festival will be going on in Silver Spring (more on that later!).

Metro’s also created another YouTube video, this one themed after a monster movie, that compares your choice of transit to how big of a carbon footprint you leave behind.

Gas prices are certainly high enough: think you’ll “dump the pump” this Thursday?