hard shoulder vs truck stop

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) 

truck stop

noun
  • A roadside service area, usually consisting of a restaurant and service station and sometimes a motel or hotel, where drivers of long-haul trucks can stop to refuel, eat, and rest. 

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