marshrutka vs tro tro

marshrutka

noun
  • A share taxi in the CIS countries, the Baltic states, and Bulgaria. The role of the modern marshrutka is similar to that of the minibus in other countries, except that some implementations of marshrutka allow passengers to stand. 

tro tro

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

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