hackney cab vs tro tro

hackney cab

noun
  • A motorised vehicle available for public hire; a black cab. 

  • A hackney carriage, a carriage pulled by a hackney horse, available for public hire. 

tro tro

noun
  • A minibus operating as a share taxi in Ghana. 

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