The US has about 1,600 miles of hydrogen pipeline today, mostly along the Gulf Coast to service oil refiner hydrogen demand. Low concentrations of hydrogen can be mixed in the existing natural gas pipeline system for transport, and existing gas pipelines may be able to be retrofit to accommodate pure hydrogen. Hydrogen can also be produced near to generation and uses of hydrogen that may not require transportation, and has the potential to reduce congestion on existing transmission system. Long distance pipeline transmission of hydrogen is a definite possibility worth continued study.
See: Hydrogen Pipelines (web page), US DOE Hydrogen and Fuel Cells Technology Office