Whether a printed ticket is required depends on the bus or train company you are traveling with.
Some only need to see a valid ID and a confirmation email or the confirmation number or the QR bar code via your mobile device which you will receive in an email from them. Some of these carriers are Amtrak, Peter Pan, Bolt Bus, Megabus, OurBus, Go Buses, Tufesa & a few others.
Others carriers do require a physical (printed) ticket with a valid photo ID in order to board. You will receive the ticket in pdf format directly from the carrier; these need to be printed out either at home, at a nearby library or paper supply store. Some of these carriers are Greyhound, Trailways NY (Adirondack/Pine Hill Kingston), Burlington Trailways, Miller Transportation, Turimex, Barons Bus Lines, Eastern Bus & a few others.
We also note on the checkout and "confirmation page" of the transaction whether or not a printed ticket is required. Please see an example below.
Trailways NY - Adirondack Trailways Bus trip:
Greyhound bus trip:
Some of Greyhound's trips also have a "pick up at station" or "will call" options which allows you to collect your ticket in person on the day of travel. A valid ID and confirmation number will be required and you are advised to arrive at the ticket office at least 45-60 minutes before the scheduled departure time.
Confirmation page (after checkout):
You can check if a U.S. bus carrier offers mobile boarding in our blog post here; https://www.wanderu.com/blog/bus-companies-mobile-boarding-guide/
If you would like more information about the individual boarding policy of the particular company you are traveling with, please use the following link to find the carriers contact information; https://www.wanderu.com/en-us/carrier/