Formal:
* Rider: This is a general term for someone who rides public transportation.
* Passenger: This emphasizes the act of traveling as a passenger.
* Traveler: This is a broader term for someone who travels, including for work or leisure.
* Pendler: This is a German word that specifically refers to someone who commutes.
Informal:
* Daily grind: This refers to the routine of commuting, often with a negative connotation.
* Rush hour warrior: This is a playful term for someone who braves the challenges of commuting during peak hours.
* Subway rider: This specifically refers to someone who uses the subway for their commute.
* Train person: This is a simple way to refer to someone who commutes by train.
The best synonym for commuter depends on the specific context and the desired level of formality.