expressway vs freeway

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. 

freeway

noun
  • A toll-free highway. 

  • A highway with grade-separated crossings (rather than level crossings) and designed (and only permitted) for high-speed motor-traffic running in two directions on one separate carriageway each 

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