back road vs overpass

back road

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

overpass

noun
  • A section of a road or path that crosses over an obstacle, especially another road, railway, etc. 

verb
  • To pass above something, as when flying or moving on a higher road. 

  • To exceed, overstep, or transcend a limit, threshold, or goal. 

  • To disregard, skip, or miss something. 

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