commuter (n.)

"one who goes back and forth to work," 1865, American English, originally "holder of a commutation ticket," agent noun from commute (v.).

A commutation ticket (1848) was a ticket issued (by a railroad, etc.) at a reduced rate entitling the holder to travel over a given route a limited number of times or an unlimited number of times over a certain period. It is from commute in its sense of "to change one kind of payment into another" (1795), especially "to combine a number of payments into a single one, pay a single sum instead of a number of successive payments" (1845).