chauffeur vs coach driver

chauffeur

noun
  • A person employed to drive a private motor car or a hired car of executive or luxury class (like a limousine). 

  • The driver of a fire truck. 

verb
  • To be, or act as, a chauffeur (driver of a motor car). 

  • To transport (someone) in a motor vehicle. 

coach driver

noun
  • A person employed to drive a coach (long-distance bus). 

  • A person driving a horse-drawn coach (carriage). 

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