back road vs service road

back road

noun
  • A secondary road, a little-used road, a road through rural areas sometimes used as an alternative to main roads. 

service road

noun
  • A relatively narrow road which runs alongside a major transportation route, such as a canal, a railway line, or a controlled-access highway. 

  • A route which enters or circulates through an institution, compound, land area, etc. for purposes of private access, maintenance, or security. 

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