Traffic mile
Traf"fic mile\ (Railroad Accounting) Any unit of the total obtained by adding the passenger miles and ton miles in a railroad's transportation for a given period; -- a term and practice of restricted or erroneous usage. Traffic mile is a term designed to furnish an excuse for the erroneous practice of adding together two things (ton miles and passenger miles) which, being of different kinds, cannot properly be added. --Hadley.