0
None needed to travel within the US.
The Corpus Callosum. You can go to Neuroscience for Kids to find answers like that.
*Actually, the Corpus Callosum is the structure, but the type of tract is commisural.
No such document is required for a US Citizen but that time will surely come someday.
The fricken book lazy
Nobody in the wiki answers community is authorized to do such thing even if they can.