The station closes at noon on Saturday and Sunday, so there is no way to print your tickets there if you bought them online. You also can't walk up and buy tickets in cash. There is no kiosk outside.
I think you can buy tickets online and choose the Pay with Cash option, and then go to a participating 7-11, get the bar code scanned and pay there, but you have to have a car or someone drive you.
So if you're paying by credit card, you have to give your ID to the driver, who then escorts you to the Union Station Ticket counter to print your ticket and get your ID back. But you can't board the bus if you are getting off at Springfield.
Thankfully, there is a CVS across the street if you have to use the bathroom, but it's a long walk! Also a Japanese restaurant next to the station. read more