hard shoulder vs sidewalk

hard shoulder

noun
  • A verge to the side of a highway, which should be used only in case of an emergency (especially on a motorway) 

sidewalk

noun
  • any paved footpath, even if not located at the side of a road 

  • (usually) a paved footpath located at the side of a road, for the use of pedestrians 

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