commuter vs commuter train

commuter

noun

  • To and from work and home. 

  • Using public transport. 

  • Normally a short form of commuter rail, commuter train or commuter bus; A transport system or a vehicle in such systems used to transport commuters (#2) 

  • One who commutes (etymology 1). 

commuter train

How often have the words commuter and commuter train occurred in a corpus of books? (source: Google Ngram Viewer )