I'm 17 and I am traveling from Laredo (Texas, US) to San Antonio (Texas). I don't have an ID, but I do have my birth certificate. Can I use that to travel by bus in Texas?
According to this page, if you are using Greyhound and you are buying a ticket online, you will need photo identification. Therefore, I believe that your birth certificate will not be enough. Here is the relevant excerpt (emphasis is mine):
Each passenger must present a ticket and a valid photo ID to board the bus.