motorway vs superhighway

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. 

superhighway

noun
  • An expressway, especially one designed for high speeds. 

  • The primary mechanism used in the movement of electronic data or information; information superhighway. 

  • A major route that carries most of the traffic going in a given direction by a specified mode of transportation. 

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