expressway vs superhighway

expressway

noun
  • A road built to freeway standards. 

  • A divided highway, especially one whose intersections and direct access to adjacent properties have been eliminated. 

  • A road built for high speed traffic, but not up to motorway standards or designated a motorway. 

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 expressway and superhighway occurred in a corpus of books? (source: Google Ngram Viewer )