Moreover, there are of course other lines that don't strictly fit into this destination. LIC <-> Greenport was once the LIRR mainline, but nowadays would be more likely described as usage:branch. LIC<-> Montauk has more of a case as an intercity line but suffers from the same ambiguity.

Would you agree then that if the line were to be reactivated to Allentown or Easton as per the Amtrak master plan that the line would be considered usage:main?

Clay,

May you clarify the technical qualifications for a line to be main vs branch? From what I know, this was the CNJ mainline from the mid 19th century through to ~1976, then the mainline of Conrail's CNJ division until 1983, when NJTransit purchased the line, where it was renamed the Raritan Valley Line. What did the line lose for it to become a branch, rather than stay a mainline?