interstate vs motorway

interstate

noun
  • A freeway that is part of the Interstate Highway System. 

adj
  • Of, or relating to two or more states. 

adv
  • Crossing states (usually provincial state, but also e.g. multinational sense). 

motorway

noun
  • A highway with grade-separated crossings (rather than level crossings) and designed (and only permitted) for high-speed motor-traffic (in Europe motor vehicles with a higher speed limit than 40 km/h) running in two directions on one separate carriageway each 

  • A racetrack venue designated especially for the sport of auto racing. 

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